add rubygem-ruby2ruby to comps

addressing:
Could not find gem 'ruby2ruby (>= 2.0.1)', required by 'safemode (~> 1.1.0)', in any of the sources

and Fedora contains 2.0.1 only in Fedora 19
Merge pull request #1345 from xsuchy/pull-req-rubygem-ruby2ruby

add rubygem-ruby2ruby to comps