Update CONTRIBUTING.md

Author: GrahamCampbell

.github/CONTRIBUTING.md

@@ -6,7 +6,7 @@ We accept contributions via pull requests on Github. Please review these guideli
 
 ## Guidelines
 
-* Please follow the [PSR-2 Coding Style Guide](https://www.php-fig.org/psr/psr-2/)..
+* Please follow the [PSR-2 Coding Style Guide](https://www.php-fig.org/psr/psr-2/).
 * Ensure that the current tests pass, and if you've added something new, add the tests where relevant.
 * Send a coherent commit history, making sure each individual commit in your pull request is meaningful.
 * You may need to [rebase](https://git-scm.com/book/en/v2/Git-Branching-Rebasing) to avoid merge conflicts.