Bump rails to 4.1.6

This keeps the app current and up-to-date with security patches.
Merge pull request #22 from alphagov/bump-rails-to-4.1.6

Bump rails to 4.1.6
Bump rails to 4.2.0

This keeps the app current and up-to-date with security patches.
Update deprecated config to silence warnings
Update spring to latest
Update rails-api to latest
Update sidekiq and airbrake gems to latest
Update test gems to latest
Update shoulda-matchers to latest
Update rspec-collection_matchers to latest
Update gds_zendesk to latest
Update gds-api-adapters to latest
Update whenever gem to latest
Update logstasher to latest