Lyft’s shares tanked 17% on Wednesday after a soft forecast for the key summer quarter stirred worries that it may be losing ground to rival Uber.Uber, which reported strong results on Tuesday, and Lyft are locked in a tussle for market share in the North American ride-hailing sector.Benefiting from a global footprint and wider array of services, Uber has been wooing customers with subscription offerings while Lyft doubled down on competitive fares as well as company-wide cost cuts to boost its business.“Ly ...