Add Android dot files to .gitignore (facebook#27589)

Summary:
Added dot files to `.gitignore` these got generated opening the project in Android Studio or running Gradle scripts.

<img width="570" alt="Screen Shot 2019-12-21 at 4 05 36 PM" src="https://user-images.githubusercontent.com/8675043/71315203-48ee3680-240c-11ea-9600-218e11b194b5.png">

## Changelog

[Internal] [Added] - Added Android Studio dot files to gitignore
Pull Request resolved: facebook#27589

Differential Revision: D19235583

Pulled By: cpojer

fbshipit-source-id: eb265d516e125aeb64807efe42832b80d7977b18

.gitignore

@@ -35,6 +35,11 @@ buck-out
 /ReactAndroid/src/main/jni/prebuilt/lib/
 /ReactAndroid/src/main/gen
 
+# Android Studio
+.project
+.settings
+.classpath
+
 # Watchman
 .watchmanconfig