Merge pull request jaredhanson#585 from ryysud/enable-more-version-on-travis

Enable node 6, 7 and 8 on Travis CI.

Author: jaredhanson

.travis.yml

@@ -1,5 +1,8 @@
 language: "node_js"
 node_js:
+  - "8"
+  - "7"
+  - "6"
   - "5"
   - "4"
   - "3" # io.js