COPYING: Fix copyright year

I suppose I shouldn't be copying these COPYING files around without at
least looking at them...
diff --git a/COPYING b/COPYING
index ebbf780..b91631b 100644
--- a/COPYING
+++ b/COPYING
@@ -1,4 +1,4 @@
-Copyright (c) 2007-2012 Yoran Heling
+Copyright (c) 2013 Yoran Heling
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the