Remove support for node 4 and 5

Author: rtfpessoa

appveyor.yml

@@ -7,8 +7,6 @@ version: "{build}"
 # What combinations to test
 environment:
   matrix:
-    - nodejs_version: 4
-    - nodejs_version: 5
     - nodejs_version: 6
     - nodejs_version: 7
     - nodejs_version: 8

circle.yml

@@ -1,7 +1,5 @@
 test:
   override:
-    - nvm install 4.8.7 && npm run test
-    - nvm install 5.12.0 && npm run test
     - nvm install 6.13.0 && npm run test
     - nvm install 7.10.1 && npm run test
     - nvm install 8.9.4 && npm run test

package.json

@@ -28,7 +28,7 @@
     "codacy-coverage": "./bin/codacy-coverage.js"
   },
   "engines": {
-    "node": ">= 4.0.0"
+    "node": ">= 6.0.0"
   },
   "dependencies": {
     "bluebird": "^3.5.x",