Merge pull request #1053 from sjackman/patch-1

PULL_REQUEST_TEMPLATE.md: Fix CONTRIBUTING.md link

.github/PULL_REQUEST_TEMPLATE.md

-- [ ] Have you followed the guidelines in our [Contributing](https://github.com/Homebrew/brew/blob/master/.github/CONTRIBUTING.md) document?
+- [ ] Have you followed the guidelines in our [Contributing](https://github.com/Homebrew/brew/blob/master/CONTRIBUTING.md) document?
 - [ ] Have you checked to ensure there aren't other open [Pull Requests](https://github.com/Homebrew/brew/pulls) for the same change?
 - [ ] Have you added an explanation of what your changes do and why you'd like us to include them?
 - [ ] Have you written new tests for your changes? [Here's an example](https://github.com/Homebrew/homebrew/pull/49031).