Update Mattermost to 5.14.2
Mattermost 5.14.1/5.14.2 contain some bug fixes to fix some accessibility issues and a web app crash when searching by date. The full changelog for them is here.
There is a Mattermost 5.14.3 that was just cut, but it only contains fixes for Mattermost EE, so it doesn't affect the version bundled with GitLab.