update to rails 4.0.4 to fix security vuln

Hey guys,

Wanted to get a discussion started around updating gems in this repo. There are a couple security vulnerabilities in rails 4.0.2 that have since been patched.

- https://groups.google.com/forum/#!topic/rubyonrails-security/Wu96YkTUR6s
- https://groups.google.com/forum/#!topic/rubyonrails-security/tfp6gZCtzr4

I have not run any tests against this change, so I would recommend doing that if you want to merge this.