title: vue.js Toast is not defined(while using mint-ui)
body: <p>toast is mint-ui component,i already import mint-ui but when i use toast in vue instance will report an error?why?</p>
  
  <pre><code>import Vue from 'vue';
  import MintUi from 'mint-ui';
  
  import 'mint-ui/lib/style.css'
  
  Vue.use(MintUi);
  
  new Vue({
      el:'#app',
      render:(creater)=&gt; creater(app),
      created(){
          new Toast('hello')  //toast is not defined
      }
  })
  </code></pre>