removed yarn dependency, npm is fast enough

.travis.yml

 install:
         # node:
   - source ./scripts/env/installNode.sh
-        # yarn:
-  - source ./scripts/env/installYarn.sh
-  - yarn config set cache-folder $YARN_CACHE
         # android sdk:
   - source ./scripts/env/installAndroidSDK.sh
         # fbsimctl:

CONTRIBUTING.md

 nvm use stable
 ```
 
-* Latest stable Yarn:
-
-```
-curl -o- -L https://yarnpkg.com/install.sh | bash
-export PATH=$PATH:$HOME/.yarn/bin
-```
-
 * Android SDK:
 
 ```
 1. Install dependencies:
 
     ```
-    yarn install
+    npm install
     ```
 
 1. Run the playground project in Android and iOS so that you can get a feel for the project.
-  
-    1. `yarn start` to get the package running in a terminal, leave it open
 
-    1. iOS: `yarn xcode` & run the project from XCode
-    
-    1. Android: Open the app in Android Studio and click `Run`   
+    1. `npm run start` to get the package running in a terminal, leave it open
+
+    1. iOS: `npm run xcode` & run the project from XCode
+
+    1. Android: Open the app in Android Studio and click `Run`
 
 1. Run the tests. Before you start changing things, make sure everything works.
 
      ```
-     yarn test-all
+     npm run test-all
      ```
 
 ## Troubleshooting
 
 * If the tests fail with an error like `Ineligible destinations for the "ReactNativeNavigation" scheme`, double check that you have the latest XCode installed.
 * If the tests fail because an Android emulator isn't available (something like `com.android.builder.testing.api.DeviceException: No connected devices!`), start the Android project from Android Studio and leave the emulator running, then try again.
-* If the tests fail with an error such as: 
+* If the tests fail with an error such as:
 
 ```js
 
 SyntaxError: Unexpected token (
 
 ```
-    
+
 You probably have an old node version which doesn't support async functions. Update your node using nvm according to the instructions above.
 
 ## Workflow
 
 | Command | Description |
 | ------- | ----------- |
-| `yarn install` | installs dependencies |
-| `yarn clean` | cleans all build directories, stops packager, fixes flakiness by removing watchman cache, etc. |
-| `yarn start` | starts the react-native packager for local debugging |
-| `yarn xcode` | for convenience, opens xcode in this project |
-| `yarn install-android`  |  builds playground debug/release version and installs on running android devices/emulators. <br> **Options:** `-- release` |
-| `yarn uninstall-android` | uninstalls playground from running android devices/simulators |
-| `yarn test-js` | runs javascript tests and coverage report |
-| `yarn test-watch` | runs javascript tests in watch mode (can also use the provided wallaby config) |
-| `yarn test-unit-ios` | runs ios unit tests in debug/release <br> **Options:** `-- release` |
-| `yarn test-unit-android` | runs android unit tests in debug/release <br> **Options:** `-- release` |
-| `yarn test-e2e-ios` | runs the ios e2e suite (with detox) in debug/release |
-| `yarn test-e2e-android` | runs the android e2e suite (with uiautomator) in debug/release on running devices/emulators <br> **Options:** `-- [release] [just com.TestClass#testMethod]` |
-| `yarn test-all` | runs all tests in parallel |
+| `npm install` | installs dependencies |
+| `npm run clean` | cleans all build directories, stops packager, fixes flakiness by removing watchman cache, etc. |
+| `npm run start` | starts the react-native packager for local debugging |
+| `npm run xcode` | for convenience, opens xcode in this project |
+| `npm run install-android`  |  builds playground debug/release version and installs on running android devices/emulators. <br> **Options:** `-- release` |
+| `npm run uninstall-android` | uninstalls playground from running android devices/simulators |
+| `npm run test-js` | runs javascript tests and coverage report |
+| `npm run test-watch` | runs javascript tests in watch mode (can also use the provided wallaby config) |
+| `npm run test-unit-ios` | runs ios unit tests in debug/release <br> **Options:** `-- release` |
+| `npm run test-unit-android` | runs android unit tests in debug/release <br> **Options:** `-- release` |
+| `npm run test-e2e-ios` | runs the ios e2e suite (with detox) in debug/release |
+| `npm run test-e2e-android` | runs the android e2e suite (with uiautomator) in debug/release on running devices/emulators <br> **Options:** `-- [release] [just com.TestClass#testMethod]` |
+| `npm run test-all` | runs all tests in parallel |
 

INSTALLING.md

 # Installing
 
 ### Add dependency
-`yarn add react-native-navigation@alpha`
+`npm install --save react-native-navigation@alpha`
 
 ### Configure Xcode
 drag-drop `node_modules/react-native-navigation/lib/ios/ReactNativeNavigation.xcodeproj` into Libraries folder in xcode (along the rest of react)

README.md

 ### Installation
 1. Download react-native-navigation v2
 ```bash
-yarn add react-native-navigation@alpha
+npm install --save react-native-navigation@alpha
 ```
 ##### iOS
 2. In Xcode, in Project Navigator (left pane), right-click on the `Libraries` > `Add files to [project name]`. Add `./node_modules/react-native-navigation/lib/ios/ReactNativeNavigation.xcodeproj` ([screenshots](https://facebook.github.io/react-native/docs/linking-libraries-ios.html#step-1))

scripts/env/installYarn.sh

-#!/bin/bash -e
-
-brew install yarn

scripts/test.all.js

 const exec = require('shell-utils').exec;
 
 async function run() {
-  exec.execSync(`yarn run clean`);
-  exec.execSync(`yarn run test-js`);
-  exec.execAsyncSilent(`yarn run start`);
-  await exec.execAsyncAll(`yarn run test-unit-android`, `yarn run test-unit-ios`);
-  await exec.execAsyncAll(`yarn run test-e2e-android`, `yarn run test-e2e-ios`);
-  exec.execSync(`yarn run clean`);
+  exec.execSync(`npm run clean`);
+  exec.execSync(`npm run test-js`);
+  exec.execAsyncSilent(`npm run start`);
+  await exec.execAsyncAll(`npm run test-unit-android`, `npm run test-unit-ios`);
+  await exec.execAsyncAll(`npm run test-e2e-android`, `npm run test-e2e-ios`);
+  exec.execSync(`npm run clean`);
   console.log('ALL PASSED!!!');
 }
 

scripts/test.e2e.android.js

 
 const release = _.includes(process.argv, 'release');
 
-// Run just a single test, e.g. yarn test-e2e-android -- just com.MyClass#myMethod
+// Run just a single test, e.g. npm test-e2e-android -- just com.MyClass#myMethod
 const filter = _(process.argv).dropWhile((a) => a !== 'just').take(2).last();
 
 run();
 }
 
 function runTests() {
-  exec.execSync(`yarn run uninstall-android`);
-  exec.execSync(`yarn run install-android ${release ? '-- release' : ''}`);
+  exec.execSync(`npm run uninstall-android`);
+  exec.execSync(`npm run install-android ${release ? '-- release' : ''}`);
   const filterParam = filter ? '-Pandroid.testInstrumentationRunnerArguments.class=' + filter : '';
   exec.execSync(`cd AndroidE2E && ./gradlew ${filterParam} connectedDebugAndroidTest`);
 }

scripts/travis.sh

   echo -e "${green}\t\t\t --> $(($duration / 60)) minutes and $(($duration % 60)) seconds ${nocolor}\n"
 }
 
-run_f "yarn install"
-run_f "yarn run clean"
-run_f "yarn run test-js"
-run_f "yarn run test-unit-android -- release"
-run_f "yarn run test-unit-ios -- release"
-run_f "yarn run test-e2e-android -- release"
-run_f "yarn run test-e2e-ios -- release"
-run_f "yarn run release"
+run_f "npm install"
+run_f "npm run clean"
+run_f "npm run test-js"
+run_f "npm run test-unit-android -- release"
+run_f "npm run test-unit-ios -- release"
+run_f "npm run test-e2e-android -- release"
+run_f "npm run test-e2e-ios -- release"
+run_f "npm run release"

v1tov2diff.md

 ### Installation
 1. Download react-native-navigation v2
 ```bash
-yarn add react-native-navigation@alpha
+npm install --save react-native-navigation@alpha
 ```
 ##### iOS
 2. In Xcode, in Project Navigator (left pane), right-click on the `Libraries` > `Add files to [project name]`. Add `./node_modules/react-native-navigation/lib/ios/ReactNativeNavigation.xcodeproj` ([screenshots](https://facebook.github.io/react-native/docs/linking-libraries-ios.html#step-1))