An insurance company did not cheat customers holding auto policies when it gave them a 20% discount on one month’s premium, a federal judge held.In a written opinion this week, U.S. District Judge Manish S. Shah threw out a proposed class-action lawsuit accusing Progressive Universal Insurance Co. of committing fraud and acting in bad faith when it offered policyholders a purportedly inadequate credit while assuring them they had the insurance company’s support.The two policyholders who filed the suit maintain Progressive …