The retail giant's quarterly results came up a bit short on the top line.Shares of Costco Wholesale (COST -1.99%) were heading lower Friday after its fiscal fourth-quarter revenue came in slightly below estimates.Ahead of Thursday afternoon's report, the warehouse retailer was trading at a lofty valuation, so a pullback on its slight miss wasn't a surprise.As of 10:51 a.m. ET Friday, the stock was down 1.5% after having fallen by as much as 3% earlier in the session. Costco is solid, but it trades at a pre ...