Update tests for new Braintree API

These new URLs were introduced in Braintree 2.32.0:

https://github.com/braintree/braintree_ruby/commit/c2575028d1f2f2cd2b025f56b0112acb3697e5dc#diff-9

This PR would also require a higher version of Braintree...but I assume people using an old version of the gem are seeing breakages anyway.
If you are just setting up the code an then calling it, does it even make sense to wrap it in a function?