[major] Drop support for Node.js 4

Author: lpinca

.travis.yml

@@ -2,9 +2,7 @@ language: node_js
 sudo: false
 node_js:
   - "10"
-  - "9"
   - "8"
   - "6"
-  - "4"
 after_success:
   - "npm install coveralls@3 && nyc report --reporter=text-lcov | coveralls"

appveyor.yml

@@ -1,10 +1,8 @@
 environment:
   matrix:
     - nodejs_version: "10"
-    - nodejs_version: "9"
     - nodejs_version: "8"
     - nodejs_version: "6"
-    - nodejs_version: "4"
 platform:
   - x86
   - x64