build: fix postinstall script causing user install errors

.github/CONTRIBUTING.md

@@ -41,9 +41,10 @@ After cloning the repo, run:
 
 ``` bash
 $ npm install
+& npm run setup
 ```
 
-This will also run the `postinstall` script which links two git hooks:
+The `setup` script links two git hooks:
 
 - `pre-commit`: runs ESLint on staged files.
 - `commit-msg`: validates commit message format (see below).

package.json

@@ -37,7 +37,7 @@
     "release": "bash build/release.sh",
     "release:weex": "bash build/release-weex.sh",
     "release:note": "node build/gen-release-note.js",
-    "postinstall": "node build/install-hooks.js",
+    "setup": "node build/install-hooks.js",
     "commit": "git-cz"
   },
   "repository": {