Update gradle plugin to 3.1.2
Update gradle plugin to 3.1.2

Change-Id: Id27c48c2b6a46c48f30968affdf38790348a3138

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