Rails Tutorial book update

I've updated the Ruby on Rails Tutorial to use the latest version of Rails 3.0 (3.0.9 as of today) in preparation for the upcoming release of a short supplementary chapter (and screencast) on Rails 3.1. There are lots of miscellaneous changes in this update of the book, including new versions of RSpec, Spork, and RubyGems itself. To update your sample application, take a look at the sample app's updated Gemfile or the full sample app on GitHub.