Form: fix blur validation

packages/form/src/form-item.vue

@@ -32,6 +32,7 @@
 <script>
   import AsyncValidator from 'async-validator';
   import emitter from 'element-ui/src/mixins/emitter';
+  import objectAssign from 'element-ui/src/utils/merge';
   import { noop, getPropByPath } from 'element-ui/src/utils/util';
 
   export default {
@@ -235,7 +236,7 @@
 
         return rules.filter(rule => {
           return !rule.trigger || rule.trigger.indexOf(trigger) !== -1;
-        });
+        }).map(rule => objectAssign({}, rule));
       },
       onFieldBlur() {
         this.validate('blur');