Merge branch 'master' of github.com:celery/celery

CONTRIBUTORS.txt

@@ -224,3 +224,4 @@ Viktor Holmqvist, 2016/12/02
 Rick Wargo, 2016/12/02
 zhengxiaowai, 2016/12/07
 Michael Howitz, 2016/12/08
+Andreas Pelme, 2016/12/13