Use reflect_on_association, rather than referring to reflections directly (https://github.com/rails/rails/issues/16928)
Test against latest Ruby 2.1 version
Merge pull request #105 from gocardless/rails-4.2

Use reflect_on_association, rather than referring to reflections directly
Merge pull request #106 from gocardless/test-against-latest-ruby-2.1

Test against latest Ruby 2.1 version
Add Travis build matrix and test against Rails 4.2