Regulars at The Nitro Bar in Providence have come to expect a line out the door as they await their weekly dose of caffeine. In its eight years, the business – which now has three operating locations in Rhode Island – has become a “hot commodity,” Nitro Bar regular Becca Day told The Herald. Day, who just moved to Providence a few months ago, attributed her constant visits to the coffee shop’s unique environment, rotation of seasonal flavors and kind employees.