[new feature] Button: add touchstart event (#3039)

packages/number-keyboard/demo/index.vue

@@ -1,7 +1,7 @@
 <template>
   <demo-section>
     <demo-block :title="$t('default')">
-      <van-button @touchstart.native.stop="keyboard = 'default'">
+      <van-button @touchstart.stop="keyboard = 'default'">
         {{ $t('button1') }}
       </van-button>
 
@@ -16,7 +16,7 @@
     </demo-block>
 
     <demo-block :title="$t('custom')">
-      <van-button @touchstart.native.stop="keyboard = 'custom'">
+      <van-button @touchstart.stop="keyboard = 'custom'">
         {{ $t('button2') }}
       </van-button>
 

packages/number-keyboard/en-US.md

@@ -12,7 +12,7 @@ Vue.use(NumberKeyboard);
 #### Default Style
 
 ```html
-<van-button @touchstart.native.stop="show = true">
+<van-button @touchstart.stop="show = true">
   Show Keyboard
 </van-button>
 

packages/number-keyboard/zh-CN.md

@@ -12,7 +12,7 @@ Vue.use(NumberKeyboard);
 #### 默认样式
 
 ```html
-<van-button @touchstart.native.stop="show = true">
+<van-button @touchstart.stop="show = true">
   弹出默认键盘
 </van-button>