Update PC180 (Uses a markdown formatter) with the new repo for mdformat (hukkin/mdformat) (#562)

Update PC180 with the new repo for mdformat

Author: tsvikas

src/sp_repo_review/checks/precommit.py

@@ -134,6 +134,7 @@ class PC180(PreCommit):
     repos = {
         "https://github.com/rbubley/mirrors-prettier",
         "https://github.com/executablebooks/mdformat",
+        "https://github.com/hukkin/mdformat",
     }