Nike has Tim Cook to thank for its warm, festive glow this Christmas. The sneaker giant disclosed in a filing that Cook, a longtime member of Nike's board and its lead independent director, bought shares in Nike worth about $3 million.Cook's purchase of 50,000 shares almost doubled his holdings in the company to just over 105,000 shares, or about$6 million. Nike's stock jumped 4.64% at the close of trading on Wednesday.Cook's investment sends a signal of support to Nike CEO Elliott Hill, who is in the mi ...