Fix broken user link in email

lib/gitlab/markdown.rb

@@ -167,7 +167,7 @@ module Gitlab
 
     def reference_user(identifier)
       if member = @project.team_members.find { |user| user.username == identifier }
-        link_to("@#{identifier}", user_path(identifier), html_options.merge(class: "gfm gfm-team_member #{html_options[:class]}")) if member
+        link_to("@#{identifier}", user_url(identifier), html_options.merge(class: "gfm gfm-team_member #{html_options[:class]}")) if member
       end
     end