fixed crashing release builds: apply react.gradle to enable bundling in release builds.

example/android/app/build.gradle

@@ -1,6 +1,7 @@
 apply plugin: "com.android.application"
 
 import com.android.build.OutputFile
+apply from: "../../node_modules/react-native/react.gradle"
 
 /**
  * Set this to true to create two separate APKs instead of one: