Fix wrong link in CONTRIBUTING.md

CONTRIBUTING.md

@@ -421,7 +421,7 @@ request is as follows:
 
 1. Fork the project into your personal space on GitLab.com
 1. Create a feature branch, branch away from `master`
-1. Write [tests](https://gitlab.com/gitlab-org/gitlab-development-kit#running-the-tests) and code
+1. Write [tests](https://docs.gitlab.com/ee/development/rake_tasks.html#run-tests) and code
 1. [Generate a changelog entry with `bin/changelog`][changelog]
 1. If you are writing documentation, make sure to follow the
    [documentation styleguide][doc-styleguide]