BOSTON — The average price for gasoline in Massachusetts has dropped again and has now matched the lowest price for 2015.AAA Northeast said Monday that its latest survey found self-serve regular unleaded selling for an average of $2.06 per gallon in the Bay State, down a penny from last week.The average price has fallen 8 cents in the past month and is 13 cents below the national average of $2.19 per gallon.