Bump rails to 4.2.0, upgrade many dependencies

This PR updates rails to 4.2.0 in order to:

* stay current
* pick up the ActiveJob and GlobalID integration

I also bumped many of the dependencies to latest because I was looking for the source of a deprecation (which turned out to be `rails-api`, which [still has an outstanding PR to fix the deprecation](https://github.com/rails-api/rails-api/pull/178)).