adding node 7 to travis config

Author: shellscape

.travis.yml

@@ -1,8 +1,9 @@
 sudo: false
 language: node_js
 node_js:
-  - "6"
   - "4"
+  - "6"
+  - "7"
 script: npm run travis
 after_success:
   - cat ./coverage/coverage.json | node_modules/codecov.io/bin/codecov.io.js