Update pull_request_template.md

Author: mcbarton

.github/pull_request_template.md

@@ -29,9 +29,7 @@ Please describe the test(s) that you added and ran to verify your changes.
 - [ ] New and existing unit tests pass locally with my changes
 - [ ] I have used understandable variable names
 - [ ] I have squashed my commits into a single commit ready for review
-- [ ] I have run `git-clang-format` on my changes
+- [ ] I have run `git-clang-format HEAD~` on my changes
 - [ ] I have made corresponding changes to the documentation
 - [ ] I have performed a self-review of my own code
 - [ ] I have commented my code, particularly in hard-to-understand areas
-- [ ] My changes generate no new warnings
-