chore(travis): whitelist greenkeeper branches

greenkeeper[bot] · greenkeeper[bot] · commit 626530ca7caf · 2017-06-04T17:57:37.000Z
diff --git a/.travis.yml b/.travis.yml
@@ -16,3 +16,4 @@ after_success:
 branches:
   only:
     - master
+    - /^greenkeeper/.*$/
