Update android.js

Fixed android build failure

Author: SaeedZhiany

templates/android.js

@@ -1,6 +1,9 @@
 module.exports = platform => [{
   name: () => `${platform}/build.gradle`,
   content: ({ packageIdentifier }) => `buildscript {
+    ext.safeExtGet = {prop, fallback ->
+        rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
+    }
     repositories {
         google()
         jcenter()
@@ -9,21 +12,17 @@ module.exports = platform => [{
     dependencies {
         // Matches the RN Hello World template
         // https://github.com/facebook/react-native/blob/1e8f3b11027fe0a7514b4fc97d0798d3c64bc895/local-cli/templates/HelloWorld/android/build.gradle#L8
-        classpath 'com.android.tools.build:gradle:3.3.2'
+        classpath("com.android.tools.build:gradle:${safeExtGet('gradlePluginVersion', '3.4.1')}")
     }
 }
 
 apply plugin: 'com.android.library'
 apply plugin: 'maven'
 
-def safeExtGet(prop, fallback) {
-    rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
-}
-
-def DEFAULT_COMPILE_SDK_VERSION = 27
-def DEFAULT_BUILD_TOOLS_VERSION = "27.0.3"
+def DEFAULT_COMPILE_SDK_VERSION = 28
+def DEFAULT_BUILD_TOOLS_VERSION = "28.0.3"
 def DEFAULT_MIN_SDK_VERSION = 16
-def DEFAULT_TARGET_SDK_VERSION = 27
+def DEFAULT_TARGET_SDK_VERSION = 28
 
 android {
   compileSdkVersion safeExtGet('compileSdkVersion', DEFAULT_COMPILE_SDK_VERSION)