refactor(search): update demo to model value

example/pages/search/index.wxml

@@ -1,18 +1,16 @@
 <demo-block title="基本用法">
   <van-search
-    value="{{ value }}"
+    model:value="{{ value }}"
     placeholder="请输入搜索关键词"
-    bind:change="onChange"
     bind:search="onSearch"
   />
 </demo-block>
 
 <demo-block title="事件监听">
   <van-search
-    value="{{ value }}"
+    model:value="{{ value }}"
     show-action
     placeholder="请输入搜索关键词"
-    bind:change="onChange"
     bind:search="onSearch"
     bind:cancel="onCancel"
     bind:clear="onClear"
@@ -21,7 +19,7 @@
 
 <demo-block title="搜索框内容对齐">
   <van-search
-    value="{{ value }}"
+    model:value="{{ value }}"
     input-align="center"
     placeholder="请输入搜索关键词"
   />
@@ -30,14 +28,14 @@
 <demo-block title="禁用搜索框">
   <van-search
     disabled
-    value="{{ value }}"
+    model:value="{{ value }}"
     placeholder="请输入搜索关键词"
   />
 </demo-block>
 
 <demo-block title="自定义背景色">
   <van-search
-    value="{{ value }}"
+    model:value="{{ value }}"
     shape="round"
     background="#4fc08d"
     placeholder="请输入搜索关键词"
@@ -46,12 +44,11 @@
 
 <demo-block title="自定义按钮">
   <van-search
-    value="{{ value }}"
+    model:value="{{ value }}"
     label="地址"
     shape="round"
     placeholder="请输入搜索关键词"
     use-action-slot
-    bind:change="onChange"
     bind:search="onSearch"
   >
     <view slot="action" bind:tap="onClick">搜索</view>