Added engines to package.json, run Node v4 and v6 on Travis

Author: montogeek

.travis.yml

@@ -1,8 +1,7 @@
 language: node_js
 node_js:
-  - "0.10"
-  - "0.12"
-  - "iojs"
+  - "4"
+  - "6"
 script: npm run travis
 
 before_install:

package.json

@@ -14,6 +14,9 @@
     "cover": "istanbul cover node_modules/mocha/bin/_mocha",
     "travis": "npm run cover -- --report lcovonly"
   },
+  "engines": {
+    "node": ">=4.3.0 <5.0.0 || >=5.10"
+  },
   "repository": {
     "type": "git",
     "url": "https://github.com/webpack/memory-fs.git"