Update Rails to avoid extremely critical security fixes

More info:
http://weblog.rubyonrails.org/2013/1/8/Rails-3-2-11-3-1-10-3-0-19-and-2-3-15-have-been-released/
Update rails and json gems to avoid security vulnerabilities

More info:
http://weblog.rubyonrails.org/2013/2/11/SEC-ANN-Rails-3-2-12-3-1-11-and-2-3-17-have-been-released/