Add third pattern to parse_issue_ref_from_message() to support the mixed
format 'gitserver/owner/repo#number' (e.g., git.fbrns.co/shoko/kugetsu#116).
Previously only two formats were supported:
1. Full URL: #116
2. Short format: shoko/kugetsu#116
Now supports:
3. Mixed format: git.fbrns.co/shoko/kugetsu#116
Fixes#144