🐛(component): [dropdown]修复 popupContainer 不适用于 vue 自身渲染的元素的问题

package/document-component/src/document/zh-CN/components/dropdown.md

@@ -23,6 +23,17 @@
         </lay-dropdown-menu>
     </template>
   </lay-dropdown>
+   &nbsp;&nbsp;
+  <lay-dropdown popupContainer=".layui-body">
+    <lay-button type="primary">下拉菜单</lay-button>
+    <template #content>
+        <lay-dropdown-menu>
+          <lay-dropdown-menu-item>选项一</lay-dropdown-menu-item>
+          <lay-dropdown-menu-item>选项二</lay-dropdown-menu-item>
+          <lay-dropdown-menu-item>选项三</lay-dropdown-menu-item>
+        </lay-dropdown-menu>
+    </template>
+  </lay-dropdown>
 </template>
 
 <script>