[Bug Report] form uses'el-select'below, and when'multiple' is'true', the'size'attribute cannot be set.

[zihe-xu]

Element UI version

2.4.11

OS/Browsers version

mac/Chrome

Vue version

2.5.21

Reproduction Link

https://jsfiddle.net/xslmenghuan/y3zc2der/6/

Steps to reproduce

<el-form ref="form" :model="form" label-width="80px">
  <el-form-item label="活动区域">
   <el-select size='mini' multiple  v-model="form.region" placeholder="请选择活动区域11">
     ...
   </el-select>
  </el-form-item>
</el-form>

What is Expected?

el-select 的 multiple、size 属性，可以同时存在

What is actually happening?

当 el-select 设置 multiple 为 true 时， 可以使用 size 属性

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.