Bump LICENSE year range

Author: svaarala

LICENSE.txt

@@ -4,7 +4,7 @@ Duktape license
 
 (http://opensource.org/licenses/MIT)
 
-Copyright (c) 2013-2019 by Duktape authors (see AUTHORS.rst)
+Copyright (c) 2013-present by Duktape authors (see AUTHORS.rst)
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal