[Bug Report] el-date-picker控制台警告：Instead, use a data or computed property based on the prop's value. Prop being mutated: "placement" #21905
Description
Element UI version
2.15.9
OS/Browsers version
Mac
Vue version
2.6.14
Reproduction Link
https://codepen.io/elanyoung/pen/abqKxqE
Steps to reproduce
打开控制台即可看到警告
What is Expected?
解决控制台警告
What is actually happening?
2.5.18版本没有此警告，更新2.5.19就出现了，placement属性造成的