cut a 2.10.12 release

See: https://github.com/github/github/issues/24484 for details.

Treading carefully here as I've never touched this gem before, so would appreciate eyes from the listed maintainers and other folks interested / knowledgeable about linguist.

/cc @github/linguist @github/languages @charliesome @piki @tnm @defunkt @vmg @bkeepers @gjtorikian @izuzak @arfon @josh @dgraham @balevine @rsese @jglovier @jonrohan @jdennes