Mattermost 4.5.1 for GitLab 10.4

@marin

I'm opening an issue to give your team a heads up that we're preparing a dot release, 4.5.1, to fix an issue where Mattermost doesn't load on certain versions of Firefox in 4.5.0.

We will prepare a merge request to GitLab omnibus in coming days, and propose it is included in an RC for GitLab 10.4.

Let me know if you have any questions.