chore(travis): whitelist greenkeeper branches

greenkeeper[bot] · flovilmart · commit 6e198a8dab5c · 2017-06-17T21:13:52.000-04:00
https://greenkeeper.io/
diff --git a/.travis.yml b/.travis.yml
@@ -3,6 +3,11 @@ language: node_js
 node_js:
 - '5'
 
+branches:
+  only:
+    - master
+    - /^greenkeeper/.*$/
+
 env:
   - CXX=g++-4.8
 
