fix: alert示例在vue2环境存在多节点报错

pages/SystemAPI/Alert/alert.vue

 <template>
+	<view>
 		<page-head :title="title"></page-head>
 		<view class="uni-padding-wrap uni-common-mt">
 			<button @tap="testShowAlert">确认框</button>
 			<button @tap="testShowPrompt">输入框</button>
 		</view>
+	</view>
+
 </template>
 
 <script>