Merge pull request #844 from yyri/master

<a-form-item> should be nested under <a-col>

ant-design-vue-jeecg/src/views/jeecg/helloworld.vue

@@ -19,11 +19,11 @@
         <a-cascader :options="areaOptions" @change="onChange" :showSearch="{filter}" placeholder="Please select" />
       </a-form-item>
       </a-col>
-      <a-form-item :wrapperCol="{ span: 12, offset: 5 }">
       <a-col :md="24" :sm="24">
+        <a-form-item :wrapperCol="{ span: 12, offset: 5 }">
           <a-button type="primary" htmlType="submit">Submit</a-button>
-        </a-col>
         </a-form-item>
+      </a-col>
     </a-form>
   </a-card>
 </template>