A sudden drop in crude-oil prices means Americans are on track to pay much less for gasoline at the pump this summer—in some cases less than $2 a gallon. Gasoline prices are typically expected to rise this time of year due to higher demand and the requirement that gas stations use a more expensive blend of fuel that won’t ignite in hot weather. And a month ago, the average U.S. pump price hit a seven-month high at $2.89 a gallon, seemingly destined for $3. …