Merge pull request #3254 from xiaofengsha/pr002

采用 findComponentUpward 替代 this.$parent.$parent.$parent 获取 Dropdown 父节点组件

src/components/dropdown/dropdown-item.vue

@@ -3,7 +3,7 @@
 </template>
 <script>
     const prefixCls = 'ivu-dropdown-item';
-
+    import { findComponentUpward } from '../../utils/assist';
     export default {
         name: 'DropdownItem',
         props: {
@@ -37,7 +37,7 @@
         },
         methods: {
             handleClick () {
-                const $parent = this.$parent.$parent.$parent;
+                const $parent = findComponentUpward(this, 'Dropdown');
                 const hasChildren = this.$parent && this.$parent.$options.name === 'Dropdown';
 
                 if (this.disabled) {