Changed the Gemfile to be Jruby compatible.

[rebelwarrior]

Yay thanks to a wonderful email from parnt; here is the pull request for the Gemfile to be Jruby compatible.

[malclocke]

You are very privileged to receive a lovely email from @parndt, he never sends me any!

A couple of questions:

• Do all the tests run clean for you on Jruby? I will add it as a target on Travis CI if it's likely to pass.
• Your change doesn't include any changes to Gemfile.lock, is that intentional? After running bundle install in my working copy I have the new gems added to Gemfile.lock, but they don't install.

[parndt]

@malclocke I sent you one yesterday in pull request form :p

[parndt]

Either this, or #114, should be merged so that both can be dealt with :-)