Hello,
I've upgraded Rails to 5.2.1 in Rawhide - sorry for late notice.
I do not plan to rebase it in stable Fedoras, but if you're on F28 and want to try it,
you can use my copr:
https://copr.fedorainfracloud.org/coprs/pvalena/ruby-on-rails/
Let me know if something broke.
Regards,
Pavel