Fix URL in PULL_REQUEST_TEMPLATE.md

Author: IGPenguin

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,6 @@
 ## ⚠️ Essential review checklist
 **I truthfully declare that all the following statements are true:**
-- [ ] This pull requests follows [the contribution rules](https://github.com/IGPenguin/hmm/blob/master/.github/CONTRIBUTING.md "the contribution rules").
+- [ ] This pull requests follows [the contribution rules](https://github.com/IGPenguin/hmm/blob/gh-pages/.github/CONTRIBUTING.md "the contribution rules").
 - [ ] New features are fully completed.
 - [ ] All changes have been properly tested.
 - [ ] Output formatting is satisfactory.