Removed a link from Ruby resource

Removed a link of Ruby resource http://mysite.verizon.net/hpassel/thinkruby/ as many of links in the resource return Not Found status
e.g. http://mysite.verizon.net/hpassel/thinkruby/book/ch03exer.html, http://mysite.verizon.net/hpassel/thinkruby/book/ch05exer.html