update dev setup guide

yyx990803 · yyx990803 · commit d1cd2f389824 · 2015-05-10T13:21:57.000-04:00
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
@@ -55,7 +55,7 @@ $ npm install
 To watch and auto-build `dist/vue.js` during development:
 
 ``` bash
-$ grunt watch
+$ npm run dev
 ```
 
 To lint:
