[improvement] List: improve accessibility

docs/markdown/changelog.zh-CN.md

@@ -6,6 +6,7 @@
 
 对以下组件增加了无障碍访问的支持：
 
+- List
 - Dialog
 - Slider
 - NoticeBar

packages/list/index.js

@@ -130,7 +130,7 @@ export default sfc({
 
   render(h) {
     return (
-      <div class={bem()}>
+      <div class={bem()} role="feed" aria-busy={this.loading}>
         {this.direction === 'down' && this.slots()}
         {this.loading && (
           <div class={bem('loading')} key="loading">

packages/list/test/__snapshots__/demo.spec.js.snap

@@ -15,7 +15,7 @@ exports[`renders demo correctly 1`] = `
         <div class="van-pull-refresh">
           <div class="van-pull-refresh__track" style="transition: 0ms;">
             <div class="van-pull-refresh__head"></div>
-            <div class="van-list"></div>
+            <div role="feed" class="van-list"></div>
           </div>
         </div>
       </div>