Update ProGuard rules for Gson.
Update ProGuard rules for Gson.

Also remove ProGuard rules for Commons Lang.

Change-Id: I537b91e111cb01f14615fc974aee29b2a9dca250

dbrant/apps-android-wikipedia,wikimedia/apps-android-wikipedia,dbrant/apps-android-wikipedia,wikimedia/apps-android-wikipedia,wikimedia/apps-android-wikipedia,dbrant/apps-android-wikipedia,dbrant/apps-android-wikipedia,wikimedia/apps-android-wikipedia,dbrant/apps-android-wikipedia