Use the new build env on Travis

more ram and cpu, better network, more capacity, better boot times
Merge pull request #43 from joshk/patch-1

Use the new build env on Travis
Make compatible with Rails 4.1 and bump Travis config
Address PR comments
Merge pull request #44 from gocardless/rails-4-1-compatibility

Make compatible with Rails 4.1 and bump Travis config
Add ability to record Rails request UUIDs