update gradle

example/android/app/build.gradle

 
 android {
     compileSdkVersion 25
-    buildToolsVersion "25.0.1"
+    buildToolsVersion '26.0.2'
 
     defaultConfig {
         applicationId "com.example"

example/android/build.gradle

 
 buildscript {
     repositories {
+        google()
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.3.3'
+        classpath 'com.android.tools.build:gradle:3.0.1'
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files
     repositories {
         mavenLocal()
         jcenter()
+        google()
         maven {
             // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm
             url "$rootDir/../node_modules/react-native/android"

example/android/gradle/wrapper/gradle-wrapper.properties

-#Fri Jun 30 16:12:20 EDT 2017
+#Sun Jan 28 19:31:28 IST 2018
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-3.3-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.1-all.zip