Table: Fixed #3896 (#4023)

* Table: Fixed #3896

* Table: fixed filter-panel format

* Table: fixed filter-panel.vue

packages/table/src/filter-panel.vue

@@ -32,6 +32,7 @@
 
 <script type="text/babel">
   import Popper from 'element-ui/src/utils/vue-popper';
+  import { PopupManager } from 'element-ui/src/utils/popup';
   import Locale from 'element-ui/src/mixins/locale';
   import Clickoutside from 'element-ui/src/utils/clickoutside';
   import Dropdown from './dropdown';
@@ -175,6 +176,13 @@
           Dropdown.close(this);
         }
       });
+    },
+    watch: {
+      showPopper(val) {
+        if (val === true && parseInt(this.popperJS._popper.style.zIndex, 10) < PopupManager.zIndex) {
+          this.popperJS._popper.style.zIndex = PopupManager.nextZIndex();
+        }
+      }
     }
   };
 </script>