Drop node.js v4 support

.travis.yml

@@ -40,9 +40,6 @@ jobs:
     - <<: *node
       node_js: '6'
 
-    - <<: *node
-      node_js: '4'
-
     - script: npm start test.bundle test.browser
       install: npm ci # we need the native modules here
       addons:
@@ -78,9 +75,6 @@ jobs:
     - <<: *smoke
       node_js: '6'
 
-    - <<: *smoke
-      node_js: '4'
-
     - stage: precache
       script: true
 

appveyor.yml

@@ -6,7 +6,6 @@ environment:
     - nodejs_version: '9'
     - nodejs_version: '8'
     - nodejs_version: '6'
-    - nodejs_version: '4'
 install:
   - ps: Install-Product node $env:nodejs_version x64
   - set CI=true

docs/README.md

@@ -9,7 +9,7 @@
 - Ruby
 - RubyGems
 - Bundler (`gem install bundler`)
-- Node.js v4.0.0 or greater
+- Node.js v6.x or greater
 
 ## Development
 

docs/index.md

@@ -92,7 +92,7 @@ or as a development dependency for your project:
 $ npm install --save-dev mocha
 ```
 
-> To install Mocha v3.0.0 or newer with `npm`, you will need `npm` v2.14.2 or newer.  Additionally, to run Mocha, you will need Node.js v4 or newer.
+> Mocha currently requires Node.js v6.x or newer.
 
 Mocha can also be installed via [Bower](https://bower.io) (`bower install mocha`), and is available at [cdnjs](https://cdnjs.com/libraries/mocha).
 

package.json

@@ -449,7 +449,7 @@
     "_mocha": "./bin/_mocha"
   },
   "engines": {
-    "node": ">= 4.0.0"
+    "node": ">= 6.0.0"
   },
   "scripts": {
     "prepublishOnly": "nps test clean build",