On issue comment, cross-referenced update incorrect when project name has underscore

In myacct/project_one#456, added a comment that included a reference to myacct/project_two#123.

The comment in myacct/project_one#456 links correctly. The auto-update in myacct/project_two#123 is incorrectly linked as:

"mentioned in issue myacct/projectone#456_"