change ManActivity to MainApplication

hi,
you have to import native package in `MainApplication` instead of `MainActivity`

Author: mammad2c

README.md

@@ -28,7 +28,7 @@
 
 #### Android
 
-1. Open up `android/app/src/main/java/[...]/MainActivity.java`
+1. Open up `android/app/src/main/java/[...]/MainApplication.java`
   - Add `import com.proyecto26.inappbrowser.RNInAppBrowserPackage;` to the imports at the top of the file
   - Add `new RNInAppBrowserPackage()` to the list returned by the `getPackages()` method
 2. Append the following lines to `android/settings.gradle`: