NEW YORK, June 30 (Reuters) - The dollar index was lower on Friday following two straight days of gains, after economic data showed a cooling in consumer spending, raising some doubt about the potential aggressiveness of the Federal Reserve in fighting inflation. 1% in May while data for the prior month was revised to show spending accelerated by 0. In contrast, euro zone inflation data fell for a third consecutive month, but showed a small drop in underlying inflation and was unlikely to keep the European Central Bank from hiking rates at its July meeting