[new feature] Area: reset method support code param

packages/area/demo/index.vue

@@ -1,10 +1,7 @@
 <template>
   <demo-section>
     <demo-block :title="$t('basicUsage')">
-      <van-area
-        ref="area"
-        :area-list="$t('areaList')"
-      />
+      <van-area :area-list="$t('areaList')" />
     </demo-block>
 
     <demo-block :title="$t('title2')">

packages/area/en-US.md

@@ -69,7 +69,7 @@ Use ref to get area instance and call instance methods
 
 | Name | Attribute | Return value | Description |
 |------|------|------|------|
-| reset | - | - | Reset all options |
+| reset | code: string | - | Reset all options by code |
 
 ### areaList Data Structure
 

packages/area/index.js

@@ -171,8 +171,8 @@ export default sfc({
       return area;
     },
 
-    reset() {
-      this.code = '';
+    reset(code) {
+      this.code = code || '';
       this.setValues();
     }
   },

packages/area/zh-CN.md

@@ -68,7 +68,7 @@ Vue.use(Area);
 
 | 方法名 | 参数 | 返回值 | 介绍 |
 |------|------|------|------|
-| reset | - | - | 重置所有选项到第一项 |
+| reset | code: string | - | 根据 code 重置所有选项，若不传 code，则重置到第一项 |
 
 ### 省市区列表数据格式