Add node v6 to travis and change 4.0, 5.0 to 4.x, 5.x

Author: LewisJEllis

.travis.yml

@@ -4,7 +4,9 @@ node_js:
   - "0.8"
   - "0.10"
   - "0.12"
-  - "4.0"
-  - "5.0"
+  - "4"
+  - "5"
+  - "6"
+  - "node"
 before_install:
   - "npm install --upgrade npm -g"