[new feature] Tabs: support switch tabs with swipe gestrue in the content (#694)

docs/demos/views/tab.vue

@@ -58,6 +58,14 @@
         </van-tab>
       </van-tabs>
     </demo-block>
+
+    <demo-block :title="$t('title8')">
+      <van-tabs :active="active" swipeable>
+        <van-tab :title="$t('tab') + index" v-for="index in tabs" :key="index">
+          {{ $t('content') }} {{ index }}
+        </van-tab>
+      </van-tabs>
+    </demo-block>
   </demo-section>
 </template>
 
@@ -71,7 +79,8 @@ export default {
       title4: '样式风格',
       title5: '点击事件',
       title6: '粘性布局',
-      title7: '自定义标签'
+      title7: '自定义标签',
+      title8: '滑动切换'
     },
     'en-US': {
       tab: 'Tab ',
@@ -81,7 +90,8 @@ export default {
       title4: 'Card Style',
       title5: 'Click Event',
       title6: 'Sticky',
-      title7: 'Custom Tab'
+      title7: 'Custom Tab',
+      title8: 'Swipeable'
     }
   },