FIX: also inline category badge styles to digest email (PR #3485)

[fantasticfears]

cc @coding-horror

Fix the broken digest email styles introduced in https://github.com/discourse/discourse/commit/54ce66fc62ee12f231d1b880e6b09910e487a5ef

GitHub

[discoursebot]

You’ve signed the CLA, fantasticfears. Thank you! This pull request is ready for review.

[SamSaffron]

thanks