Update license to GPL v2 or later, and correct copyright information.

style.css

@@ -5,13 +5,14 @@ Author URI: http://kwight.ca
 Theme URI: https://github.com/kwight/debut/
 Description: Debut is a solid and clean responsive theme, for sharing your ideas with the world. Make Debut your own by changing the background, colors and more with the new Theme Customizer and real-time preview. Based on _s by Automattic, Debut is translation-ready (French is already included), supports featured images, has five widget areas and includes a sliding menu for mobile screens. Debut also includes a full-width page template.
 Version: 1.6
-License: GNU General Public License
+License: GNU GPL v2 or later
 License URI: http://www.gnu.org/licenses/gpl-2.0.html
 Text Domain: debut
 Tags: white, black, red, gray, two-columns, one-column, flexible-width, right-sidebar, custom-background, custom-colors, custom-menu, featured-images, full-width-template, sticky-post, threaded-comments, translation-ready
 
 
-Debut (c) 2012 Kirk Wight
+Debut (c) 2012-2014 Kirk Wight.
+Underscores (c) 2012-2014 Automattic, Inc.
 
 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License