docs: update demo

example/index.js

@@ -1,16 +1,5 @@
-/* eslint-disable import/no-extraneous-dependencies */
-import Vue from 'vue';
-
-import DatePicker from '../src/index';
-
-// import '../src/locale/zh-cn';
-
-import '../src/style/index.scss';
-
 import App from './app';
 
-Vue.use(DatePicker);
-
-new Vue({
+new window.Vue({
   render: h => h(App),
 }).$mount('#app');