Bump Node.js requirement to 0.12.0

This is the latest stable release which also contains the latest npm so
there's no need for a separate requirement for it.

README.md

@@ -14,8 +14,7 @@ Sage is a WordPress starter theme based on HTML5 Boilerplate, gulp, Bower, and B
 ## Requirements
 
 * PHP >= 5.4
-* Node.js >= 0.10
-* npm >= 2.1.5 (`npm install -g npm@latest`)
+* Node.js >= 0.12.0
 * gulp (`npm install -g gulp`)
 * Bower (`npm install -g bower`)
 

package.json

@@ -23,7 +23,7 @@
     "jscs": "jscs gulpfile.js assets/scripts/*.js"
   },
   "engines": {
-    "node": ">= 0.10.0",
+    "node": ">= 0.12.0",
     "npm": ">=2.1.5"
   },
   "devDependencies": {