Dots, the extremely addictive mobile game that’s something like a delightful mix of Tetris, Connect Four, and a Rubik’s Cube, is the second most popular free iPhone app just a week after launching. It’s been downloaded more than a million times, and at least 38 million games of dots have been played, according to John Borthwick, CEO of Betaworks, the New York-based venture capital firm that owns t