[Misc] Update README development branch from stable-2.x to stable-3.x

Author: abrassat

README.md

@@ -11,4 +11,4 @@
 * Continuous Integration Status: [![Build Status](http://ci.xwikisas.com/view/All/job/xwikisas/job/application-googleapps/job/master/badge/icon)](http://ci.xwikisas.com/view/All/job/xwikisas/job/application-googleapps/job/master/)
 
 # Note
-Development is done right now on the `stable-2.x` branch. Please do your commits in this branch
+Development is done right now on the `stable-3.x` branch. Please do your commits in this branch