Update broken link in CONTRIBUTING

Previous link to the guide for resolving merge conflicts in github no
longer exist, so replaced with the next best tutorial from github docs.

CONTRIBUTING.md

@@ -61,8 +61,8 @@ When you're finished with the changes, create a pull request, also known as a PR
 Once you submit your PR, a Docs team member will review your proposal. We may ask questions or request for additional information.
 - We may ask for changes to be made before a PR can be merged, either using [suggested changes](https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/incorporating-feedback-in-your-pull-request) or pull request comments. You can apply suggested changes directly through the UI. You can make any other changes in your fork, then commit them to your branch.
 - As you update your PR and apply changes, mark each conversation as [resolved](https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/commenting-on-a-pull-request#resolving-conversations).
-- If you run into any merge issues, checkout this [git tutorial](https://lab.github.com/githubtraining/managing-merge-conflicts) to help you resolve merge conflicts and other issues.
+- If you run into any merge issues, checkout this [git tutorial](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/addressing-merge-conflicts/resolving-a-merge-conflict-on-github) to help you resolve merge conflicts and other issues.
 
 ### Your PR is merged!
 
-Congratulations :tada::tada: The Ably Labs team thanks you! :sparkles:
+Congratulations :tada::tada: The Ably Labs team thanks you! :sparkles: