Removed a link from Ruby resource

free-programming-books.md

@@ -1546,7 +1546,6 @@ See also [TeX](#tex)
 ### Ruby
 * [A community-driven Ruby style guide](https://github.com/bbatsov/ruby-style-guide)
 * [CodeCademy Ruby](http://www.codecademy.com/tracks/ruby)
-* [How To Think Like a Computer Scientist: Learning With Ruby](http://mysite.verizon.net/hpassel/thinkruby/)
 * [Just Enough Ruby to Get By](http://dmtri.com/posts/65)
 * [Learn Ruby the hard way](http://ruby.learncodethehardway.org/book/)
 * [Learn to Program, by Chris Pine](http://pine.fm/LearnToProgram/)