Install jruby-jack gem from source?

gistfile1.txt

gem uninstall jruby-rack; # get rid of old jruby-rack gem
git clone https://github.com/jruby/jruby-rack.git; # clones into jruby-rack directory
cd jruby-rack; # cd into the new directory
bundle install; # shouldn't this put the gem into the gemset?
rake install_gem; # what's this for?
# delete the git source from my rails project
cd ../; 
rm -rf jruby-jack;