[chore] cache yarn when running on travis-ci.

diasbruno · diasbruno · commit 8480042e123e · 2017-06-19T00:12:52.000-03:00
diff --git a/.travis.yml b/.travis.yml
@@ -2,6 +2,7 @@ language: node_js
 node_js:
   - "7"
   - "6"
+cache: yarn
 before_script:
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start
