support `rake gem` on RubyGems 2.0 (removed Gem::Builder)
support `rake gem` on RubyGems 2.0 (removed Gem::Builder)

jruby/jruby-rack,jruby/jruby-rack,jhstatewide/jruby-rack,jruby/jruby-rack,jruby/jruby-rack,jruby/jruby-rack,jhstatewide/jruby-rack,jhstatewide/jruby-rack,jruby/jruby-rack,jhstatewide/jruby-rack