Stop using deprecated argument to `gem`
--no-rdoc
and --no-ri
have been deprecated since RubyGems 2.0:
https://github.com/rubygems/rubygems/blob/v2.0.0/History.txt#L43
They were finally removed in a recent release: https://github.com/rubygems/rubygems/pull/2354
Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/55740 (doesn't close it; that issue is about documentation).