Lyft's guidance disappointed even as it reported its first-ever GAAP profit.Shares of Lyft (LYFT -17.23%) were taking a dive today after the No. 2 ride-sharing company posted disappointing results in its second-quarter earnings report last night.As a result, the stock closed the day down 17.2%. Q2 results were strongLyft's second-quarter results were strong, but weaker third-quarter guidance seemed to spook investors. Second-quarter revenue jumped 41% year over year to $1.44 billion, beating the consensus o ...