chore(deps): Support node 6,8,10

BREAKING CHANGE:
  Drop support for node < 6

Author: johnjbarton

.travis.yml

@@ -1,7 +1,8 @@
 sudo: false
 language: node_js
 node_js:
-  - 4
+  - "6"
+  - "8"
   - stable
 
 before_install: