chore(package.json): add gh-pages scripts

Author: 王林涛

package.json

@@ -8,7 +8,8 @@
     "dev": "node build/dev-server.js",
     "start": "node build/dev-server.js",
     "dev-dist": "node build/dev-dist.js",
-    "build": "node build/build.js"
+    "build": "node build/build.js",
+    "gh-pages": "git subtree push --prefix=examples/dist origin gh-pages"
   },
   "dependencies": {
     "vue": "^2.3.3"