Merge pull request #303 from q6112345/master

Added missing $

android/app/build.gradle

     jcenter()
     maven {
         // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm
-        url "rootDir/../node_modules/react-native/android"
+        url "$rootDir/../node_modules/react-native/android"
     }
 }