Fix balance_transaction type in IRefund
Fix balance_transaction type in IRefund

balance_transaction could be either a string or a balance.IBalanceTransaction, since it is an "Expandable".
dsebastien/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped,borisyankov/DefinitelyTyped,georgemarshall/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,mcliment/DefinitelyTyped,borisyankov/DefinitelyTyped