ci(travis): Update to node 10 (#17)

Author: gr2m

.travis.yml

@@ -4,6 +4,7 @@ cache:
     - ~/.npm
 node_js:
   - 8
+  - 10
 
 # Trigger a push build on master and greenkeeper branches + PRs build on every branches
 # Avoid double build on PRs (See https://github.com/travis-ci/travis-ci/issues/1147)