Update Peek gem once peek#113 has been merged
In https://github.com/peek/peek/pull/113, we've fixed a bug with Peek on Puma: https://gitlab.com/gitlab-org/gitlab-ce/issues/66528
As that PR hasn't been reviewed by the maintainer yet, I created https://gitlab.com/gitlab-org/gitlab-peek, pushed it to https://rubygems.org/gems/gitlab-peek, and added the owners in https://about.gitlab.com/handbook/developer-onboarding/#ruby-gems.
Once that PR has been merged and released, we can go back to using the upstream gem.