Gartner's slowing contract growth sent the stock plunging this week.Shares of Gartner (IT -0.17%) cratered this week, finishing down 30.3% from last Friday's close. The drop came as the S&P 500 and Nasdaq-100 gained 2.4% and 3.7%, respectively.Gartner, an IT- and tech-focused business insights company, reported its Q2 earnings earlier this week. Though its current quarter performance met Wall Street's expectations, investors are concerned about future growth.Gartner's contract growth slowsThe company posted ...