fix(DropdownMenu): incorrect menu position when scroll (#5313)

src/dropdown-menu/index.js

@@ -2,6 +2,7 @@ import { createNamespace } from '../utils';
 import { BORDER_TOP_BOTTOM } from '../utils/constant';
 import { ParentMixin } from '../mixins/relation';
 import { ClickOutsideMixin } from '../mixins/click-outside';
+import { getScrollEventTarget } from '../utils/dom/scroll';
 
 const [createComponent, bem] = createNamespace('dropdown-menu');
 
@@ -44,6 +45,12 @@ export default createComponent({
     };
   },
 
+  computed: {
+    scroller() {
+      return getScrollEventTarget(this.$el);
+    }
+  },
+
   methods: {
     updateOffset() {
       const { menu } = this.$refs;