Feat: Move to node 6

.travis.yml

@@ -1,7 +1,7 @@
 language: node_js
 
 node_js:
-  - '4.2.1'
+  - '6'
 
 before_install: if [[ `npm -v` != 3* ]]; then npm i -g npm@3; fi
 

CONTRIBUTING.md

@@ -61,8 +61,8 @@ If you've found a bug that is not on the board, [follow these steps](#found-a-bu
 | Prerequisite                                | Version |
 | ------------------------------------------- | ------- |
 | [MongoDB](http://www.mongodb.org/downloads) | `~ ^3`  |
-| [Node.js](http://nodejs.org)                | `~ ^4`  |
-| npm (comes with Node)                       | `~ ^2`  |
+| [Node.js](http://nodejs.org)                | `~ ^6`  |
+| npm (comes with Node)                       | `~ ^3`  |
 
 > _Updating to the latest releases is recommended_.