Fix value conversion method
Fix value conversion method

In Solidus, this method has changed from having two parameters to
having three. This updates the method here to match, so we avoid
any too_many_parameter errors. Most noticably, this was affecting
our test suite.

See: https://github.com/solidusio/solidus/commit/e05da68179b45a68d762dfcc7c1ba6618d00d234

solidusio/solidus_paypal_braintree,solidusio/solidus_paypal_braintree,solidusio/solidus_paypal_braintree,solidusio/solidus_paypal_braintree