Update jquery-ruby in Gemfile

I noticed that the jquery-ruby gem (v2.0.0) has been "yanked" according to their rubygems home page, and it was causing problems with Bundler.  Bundler kept saying it could not update nor install the Gemfile.

Thus, I updated to jquery-ruby gem (v2.0.1).  I played around with the website, and on first glance, everything still seems to work ok.

On a side note, I want to thank you for this tutorial.  It is an amazing piece of work!