Iview DatePicker 无法验证的问题，这么写就行了

<FormItem label="有效期" prop="expiretime" class="width-80">
    <DatePicker type="datetime" format="yyyy-MM-dd HH:mm:ss" placeholder="有效期" :value="formItem.expiretime" @on-change="formItem.expiretime=$event"></DatePicker>
</FormItem>