[Bug Report] date-picker placement is prop,but use as data
- Dominant language
- Vue
- Stars
- 54k
- Forks
- 14.4k
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Description
### Element UI version
2.15.9
### OS/Browsers version
chrome86.0.4240.198
### Vue version
2.6.14
### Reproduction Link
https://jsfiddle.net/osxcn/apogf8d5/3/
### Steps to reproduce
when use el-date-picker, in Console, you can find this bug.
at `packages\date-picker\src\picker.vue` line 101, 5 weeks ago, `XivLaw` add the prop 'placement', but 'placement' using at line 583 as a data.

### What is Expected?
fix this bug
### What is actually happening?
in Console, Vue warn:

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