Use the standard method for determining if the payment method is a check
Merge pull request #594 from Shopify/fix_checks

Use the standard method for determining if the payment method is a check
Bump for release
check to make sure payment_method_or_reference is not a string before trying to get card brand
Add Cybersource test for purchase by reference
Merge pull request #597 from natejgreene/master

cybersource:  Check that payment_method_or_reference is not a string before getting the card brand
Add debitCreditIndicator to amount if included in options
Bump for release 1.31.1
Paymill: Add full list of supported countries.
Fix failing tests
Merge pull request #598 from Shopify/add-debit-credit-indicator-to-worldpay

Add debitCreditIndicator to amount if included in options