Remove constraint on Prime class usage.
Remove constraint on Prime class usage.

Since this was throwing an error in new versions of Ruby it is best
to remove it since it was impacting the exercise.

NeimadTL/ruby,gchan/xruby,NeimadTL/ruby,Insti/exercism-ruby,tommyschaefer/xruby,Insti/exercism-ruby,Insti/exercism-ruby,tommyschaefer/xruby,Insti/xruby,gchan/xruby,exercism/xruby,exercism/xruby,Insti/xruby,kotp/xruby,kotp/xruby,NeimadTL/ruby