Update PULL_REQUEST_TEMPLATE.md

.github/PULL_REQUEST_TEMPLATE.md

-Please makes sure these boxes are checked before submitting your PR, thank you!
+Please make sure these boxes are checked before submitting your PR, thank you!
 
 * [ ] Make sure you follow Element's contributing guide ([中文](https://github.com/ElemeFE/element/blob/master/.github/CONTRIBUTING.zh-CN.md) | [English](https://github.com/ElemeFE/element/blob/master/.github/CONTRIBUTING.en-US.md)).
 * [ ] Make sure you are merging your commits to `dev` branch.