Update License year to 2021 (iluwatar#1639)

Co-authored-by: Ilkka Seppälä <[email protected]>

Author: ohbus

LICENSE.md

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2014-2020 Ilkka Seppälä
+Copyright (c) 2014-2021 Ilkka Seppälä
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal