Update copyright year

mmistakes · mmistakes · commit 91bb96f6ced8 · 2021-07-05T21:11:53.000-04:00
diff --git a/README.md b/README.md
@@ -954,7 +954,7 @@ grammar, etc.
 
 The MIT License (MIT)
 
-Copyright (c) 2017-2018 Michael Rose and contributors
+Copyright (c) 2017-2021 Michael Rose and contributors
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
