update PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -2,6 +2,7 @@ First of all, thanks for your contribution! :-)
 
 Please makes sure these boxes are checked before submitting your PR, thank you!
 
+* [ ] Make sure you propose PR to correct branch: bugfix for `master`, feature for latest active branch `feature-x.x`.
 * [ ] Make sure you follow antd's [code convention](https://github.com/ant-design/ant-design/wiki/Code-convention-for-antd).
 * [ ] Run `npm run lint` and fix those errors before submitting in order to keep consistent code style.
 * [ ] Rebase before creating a PR to keep commit history clear.