Compare state directly in specs.
Compare state directly in specs.

Previously this test used the invalid? method definition from state
machine which conflicted with a method from ActiveModel. Instead of
dealing with that issue, we will compare the state directly to what it
should be rather than relying upon the magic methods defined by
state_machine.

Fixes #5

Bombsheller/spree_store_credit_payment_method,Bombsheller/spree_store_credit_payment_method,Bombsheller/spree_store_credit_payment_method