Update rails to  v3.2.21

I don't believe us to be vulnerable to [CVE-2014-7829](https://groups.google.com/forum/#!topic/rubyonrails-security/rMTQy4oRCGk), but as before let's keep rails up to date.

I also had to upgrade libv8 to v3.16.14.7 as I couldn't get the locked version to compile on my computer. I don't believe this should be a problem.