GitLab upgraded

Hi everyone, Yesterday I upgraded GitLab to 12.1 and added a few patches specific to the GHC instance. There are a few effects: 1. issue and merge request numbers are now the first thing displayed in the page title of merge request and issue pages. 2. issue and merge request numbers are also shown at the beginning of email subject lines. 3. due to an apparent regression, GitLab's CI configuration validator started rejecting our .gitlab-ci.yml. I have fixed this in 5e04841c4641e2249066614065053166657e3eb4. If you see mysterious "yaml invalid" errors in your CI results you should try rebasing on to current `master`. Cheers, - Ben