chore: update copyright year

kiaking · kiaking · commit 066b5fa317c2 · 2021-01-05T22:28:18.000+09:00
diff --git a/LICENSE b/LICENSE
@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2020 Kia Ishii
+Copyright (c) 2021 Kia Ishii
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
