Fix mention notification is not sent when user pattern is leading by some punctuation marks like ! or ? (39553).

Patch by Thomas Löber.

git-svn-id: https://svn.redmine.org/redmine/branches/5.0-stable@22441 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine/acts/mentionable.rb

@@ -103,7 +103,9 @@ module Redmine
             \s|
             \]|
             <|
-            $)
+            [[:punct:]]?
+            $
+          )
         /ix
       end
     end