chore: update pull request template
<!--- Go over all the following points, and put an `x` in all the boxes that apply. -->
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-- [ ] Code compiles correctly.
-- [ ] My code follows the code style of this project.
- [ ] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.
- [ ] I have read the **CONTRIBUTING** document.
- [ ] I have added tests to cover my changes.
-- [ ] All new and existing tests passed.
