Rails 4.0.1

Rails 4.0.1 (stable) just released, and I updated `Gemfile` and `Gemfile.lock` for it. Everything in our application seems to be working okay so far.

Notes:
- Rails has performance updates! Yay!
- I only ran `bundle update` for Rails itself. Since this is a patch release and our tests are passing, I am assuming that we won't need to update any other dependencies.
- The behavior of chained ActiveRecord sorts has changed in Rails 4.0.1, back to how it worked in Rails 3.x. This also seems to be okay with our app, though.