Test different versions of Node in Travis

.travis.yml

@@ -1,7 +1,8 @@
 language: node_js
 sudo: false
 node_js:
-    - "0.12.4"
+    - "5.8"
+    - "0.12"
 before_install:
     - "npm install -g npm"
     - "npm install -g grunt-cli"