Rails 3.0.7 has been released, and the Ruby on Rails Tutorial has been updated accordingly. To upgrade an existing application, edit your Gemfile and change the Rails gem version from '3.0.6' to '3.0.7'. Then run
$ bundle update rails && bundle install
If you use the Spork gem, I also suggest editing your Gemfile to upgrade from '0.9.0.rc4' to '0.9.0.rc5'.