Updating node versions

Bumped up minimum required version to 6

Author: agnivade

.travis.yml

@@ -1,9 +1,9 @@
 sudo: false
 language: node_js
 node_js:
-  - "4"
-  - "5"
   - "6"
+  - "7"
+  - "8"
   - "stable"
 script:
   - npm run test:all

package.json

@@ -18,7 +18,7 @@
   ],
   "homepage": "http://tldr-pages.github.io",
   "engines": {
-    "node": ">=4.7"
+    "node": ">=6.12.0"
   },
   "main": "bin/tldr",
   "files": [