Test last 2 Node LTSes instead of latest version

Author: SpaceK33z

.travis.yml

@@ -1,7 +1,8 @@
 sudo: false
 language: node_js
 node_js:
-  - node
+  - "6"
+  - "4"
 script: npm run travis
 after_success:
   - cat ./coverage/coverage.json | node_modules/codecov.io/bin/codecov.io.js