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

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.

I carefully tested it, if I oversaw a port, please let me know.

Differential Revision: https://reviews.freebsd.org/D22220