Update Mermaid to v8.2.3

This fixes fill colors not working with Mermaid and pulls
in a number of other fixes.

* https://github.com/knsv/mermaid/blob/master/CHANGELOG.md
* https://github.com/knsv/mermaid/#special-note-regarding-version-82

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/64601