www/gitlab: fix regression from d747b3e47669abac14d4808212f48455fbe3f3fe

www/rubygem-js-routes 2.4.x includes in incompatible API change which
breaks gitlab at runtime while e.g. loading projects.
The problem only appears if the asset for gitlab are recompiled with
this new version which makes it harder to spot the problem.

I will follow up the issue here:
https://gitlab.com/gitlab-org/gitlab/-/work_items/605464

Thanks a lot to Peter for finding the cause of that problem!

PR: 296698
(cherry picked from commit c49ba7cf5ca1e8e12c8ff76f96f232c7ee448084)