Fix broken link to contribution guidelines

Author: bbatsov

.github/PULL_REQUEST_TEMPLATE.md

@@ -6,11 +6,13 @@ The more detailed you are, the better.**
 Before submitting a PR make sure the following things have been done (and denote this
 by checking the relevant checkboxes):
 
-- [ ] The commits are consistent with our [contribution guidelines](../CONTRIBUTING.md)
+- [ ] The commits are consistent with our [contribution guidelines][1]
 - [ ] You've added tests (if possible) to cover your change(s). Indentation & font-lock tests are extremely important!
 - [ ] All tests are passing (`make test`)
 - [ ] The new code is not generating bytecode or `M-x checkdoc` warnings
 - [ ] You've updated the changelog (if adding/changing user-visible functionality)
 - [ ] You've updated the readme (if adding/changing user-visible functionality)
 
 Thanks!
+
+[1]: https://github.com/clojure-emacs/clojure-mode/blob/master/CONTRIBUTING.md