Configure Travis CI to test on more Node.js versions

Author: kemitchell

.travis.yml

@@ -4,7 +4,9 @@ node_js:
   - "0.10"
   - "0.11"
   - "0.12"
-  - "4.2"
+  - "4"
+  - "5"
+  - "6"
   - "node"
 sudo: false
 script: [ "npm test", "npm run lint" ]