Bump Rails to 3.2.10.

Version 3.2.10 fixes a security vulnerability in ActiveRecord. See
<https://groups.google.com/forum/?fromgroups=#!topic/rubyonrails-security/DCNTNp_qjFM>
Merge pull request #46 from alphagov/bump-rails-to-3.2.10

Bump Rails to 3.2.10.