Change rubygem ports required by www/gitlab-ce to rails52

[mfechner]

Summary

Currently a lot of ports www/gitlab-ce is using pulls rails 5.0 and 5.2 ports as dependencies in.
To reduce the number of ports required, the attached patch switches all required ports to rails 5.2.

What do you think about applying such a change?

[sunpoet]

The patch itself looks OK. However, the change may work for www/gitlab-ce but break other ports. Please check all the dependent ports of above ports before you commit it. Thanks!