Fix the formatting in the PR template

Author: bbatsov

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,11 +1,11 @@
 Before submitting a PR make sure the following things have been done:
 
--[]The commits are consistent with our [contribution guidelines](CONTRIBUTING.md)
--[]You've added tests (if possible) to cover your change(s)
--[]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)
--[]You've updated the refcard (if you made changes to the commands listed there)
+- [ ] The commits are consistent with our [contribution guidelines](CONTRIBUTING.md)
+- [ ] You've added tests (if possible) to cover your change(s)
+- [ ] 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)
+- [ ] You've updated the refcard (if you made changes to the commands listed there)
 
 Thanks!