Update copyright information

* Name "cgit Development Team" as copyright holder to avoid listing
  every single developer.

* Update copyright ranges.

Signed-off-by: Lukas Fleischer <cgit@crytocrack.de>

html.c

@@ -1,6 +1,6 @@
 /* html.c: helper functions for html output
  *
- * Copyright (C) 2006 Lars Hjemli
+ * Copyright (C) 2006-2014 cgit Development Team <cgit@lists.zx2c4.com>
  *
  * Licensed under GNU General Public License v2
  *   (see COPYING for full license text)