Also release Android sources to npm

Summary:Turns out also having sources (besides binaries in /android) in npm is useful:
https://facebook.github.io/react-native/docs/android-building-from-source.html

Reviewed By: mkonicek

Differential Revision:D2947237
Ninja: oss-only

fb-gh-sync-id: 80e3e79c9c5a5f54fd54e91ac147249a68c74847
shipit-source-id: 80e3e79c9c5a5f54fd54e91ac147249a68c74847

package.json

@@ -83,6 +83,7 @@
   "files": [
     "React",
     "React.podspec",
+    "ReactAndroid",
     "android",
     "Libraries",
     "packager",