Recommend Node v4 & use as default (#126)

refs TryGhost/Ghost#7098

- Use Node v4 as our default build environment
- Change engines in package.json to match Ghost core

ghost/admin/.travis.yml

@@ -3,7 +3,7 @@ dist: trusty
 
 language: node_js
 node_js:
-  - "0.10"
+  - "4"
 
 env:
   global:
@@ -11,7 +11,7 @@ env:
 
 matrix:
   include:
-    - node_js: "0.10"
+    - node_js: "4"
       env: TEST_SUITE=lint
 
 branches:

ghost/admin/package.json

@@ -21,7 +21,7 @@
     "test": "ember test"
   },
   "engines": {
-    "node": ">= 0.10.0"
+    "node": "~0.10.0 || ~0.12.0 || ^4.2.0"
   },
   "devDependencies": {
     "bluebird": "3.4.1",