Updated rack to 1.4.5

Protects agains potential timing attacks from CVE-2013-0263
Merge pull request #112 from andrew/rack-update

Updated rack to 1.4.5
Updated rails and json gems

Following security releases outlined here:
http://weblog.rubyonrails.org/2013/2/11/SEC-ANN-Rails-3-2-12-3-1-11-and-
2-3-17-have-been-released/
Merge pull request #113 from andrew/rails-3.2.12

Updated rails and json gems