Update README.md

Ruby on Rails Tutorial link updated.

Author: duarme

README.md

@@ -67,7 +67,7 @@ independently outside Rails.
     * [Getting Started with Rails](http://guides.rubyonrails.org/getting_started.html)
     * [Ruby on Rails Guides](http://guides.rubyonrails.org)
     * [The API Documentation](http://api.rubyonrails.org)
-    * [Ruby on Rails Tutorial](http://ruby.railstutorial.org/ruby-on-rails-tutorial-book)
+    * [Ruby on Rails Tutorial](http://www.railstutorial.org/book)
 
 ## Contributing