Typo fix

I think you meant `gem install redshift`, not `gem install ruby`?

Thanks for sending me a heads-up on this, was very interesting talking with you. I'm a little surprised to see a scientific package in Ruby, but will have a go at playing with it. What I'd love to see as someone interested in doing model-based optimization, is can I dump the entire computational graph of an assembled model into an efficient compact structural representation.