Update Ruby to 2.5.3
Update Ruby from 2.4.4 to 2.5.3 to keep consistent with one in omnibus-gitlab.
as is
$ docker run --rm registry.gitlab.com/gitlab-org/gitlab-omnibus-builder/debian_9:0.0.29 ruby -v
ruby 2.4.4p296 (2018-03-28 revision 63013) [x86_64-linux]
Last update: feffb481
to be
2.5.3 (cf. omnibus-gitlab!2806 (merged))
This was found through https://gitlab.com/gitlab-org/omnibus-gitlab/blob/fd53e369dfa5e204197c9a29c3fa59c5f003cde4/doc/build/prepare-build-environment.md#setting-up-a-build-environment (omnibus-gitlab!3042 (comment 142817290)). Thanks @twk3