Shares of Stitch Fix got off to a rocky start right after the company's market debut in mid-November, but for the last week they've been on a tear. Since falling below the $15 IPO price in early days, the stock is now up more than 50 percent. Plus Roku shares are seeing similar strength since that company's IPO. The stock is now more than double where it opened in late September, and one analyst says it has more upside.