Update gradle plugin to 3.1.3
Update gradle plugin to 3.1.3

Change-Id: I5f12f5180c3914212f137e45ba3c2faec34266be

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