Drop Node 4 and Node 5 support (#495)

Author: PJSimon

.travis.yml

@@ -1,7 +1,5 @@
 language: node_js
 node_js:
-    - "4"
-    - "5"
     - "6"
     - "7"
     - "8"
@@ -13,4 +11,4 @@ branches:
         - master
 
 script: "npm test"
-after_script: "cat ./coverage/lcov.info | ./node_modules/.bin/coveralls"
+after_script: "cat ./coverage/lcov.info | ./node_modules/.bin/coveralls"