BREAKING: Drop Node 4 support

Author: RyanZim

.travis.yml

@@ -4,7 +4,6 @@ node_js:
   - node
   - 8
   - 6
-  - 4
 script:
   - npm run ci
 after_success:

appveyor.yml

@@ -1,8 +1,8 @@
 environment:
   matrix:
+    - nodejs_version: "10"
     - nodejs_version: "8"
     - nodejs_version: "6"
-    - nodejs_version: "4"
 
 version: "{build}"
 build: off

package.json

@@ -4,7 +4,7 @@
   "description": "CLI for PostCSS",
   "main": "index.js",
   "engines": {
-    "node": ">=4"
+    "node": ">=6"
   },
   "bin": {
     "postcss": "./bin/postcss"