def gem?(*args)
      options = args.last.is_a?(Hash) ? args.pop : {}
      name, requirement_string = args
      if options[:gemfile] && !process_gemfile?(options[:gemfile])
        gem_in_gemfile?(options[:gemfile], name, requirement_string)
      else
        gem_activated?(name, requirement_string)
      end
    end
def gem?(*args)
      options = args.last.is_a?(Hash) ? args.pop : {}
      name, requirement_string = args
      if options[:gemfile] && !process_gemfile?(options[:gemfile])
        gem_in_gemfile?(options[:gemfile], name, requirement_string)
      else
        gem_activated?(name, requirement_string)
      end
    end
Check if the given gem was activated by the current gemfile.
 It might or might not have been `require`d yet.

 @example
   Gemika::Env.gem?('activerecord')
   Gemika::Env.gem?('activerecord', '= 5.0.0')
   Gemika::Env.gem?('activerecord', '~> 4.2.0')