fix[complex-table]: form header sort icon is out of sync (#2382)

src/views/table/complex-table.vue

@@ -35,7 +35,7 @@
       style="width: 100%;"
       @sort-change="sortChange"
     >
-      <el-table-column label="ID" prop="id" sortable="custom" align="center" width="80">
+      <el-table-column label="ID" prop="id" sortable="custom" align="center" width="80" :class-name="getSortClass('id')">
         <template slot-scope="scope">
           <span>{{ scope.row.id }}</span>
         </template>
@@ -375,6 +375,14 @@ export default {
           return v[j]
         }
       }))
+    },
+    getSortClass: function(key) {
+      const sort = this.listQuery.sort
+      return sort === `+${key}`
+        ? 'ascending'
+        : sort === `-${key}`
+          ? 'descending'
+          : ''
     }
   }
 }