Update copyright year to 2021.

LICENSE.txt

@@ -1,4 +1,4 @@
-Copyright (c) 2017-2020, Feral Interactive
+Copyright (c) 2017-2021, Feral Interactive
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without

README.md

@@ -136,7 +136,7 @@ See the [contributors](https://github.com/FeralInteractive/gamemode/graphs/contr
 ---
 ## License
 
-Copyright © 2017-2020 Feral Interactive
+Copyright © 2017-2021 Feral Interactive
 
 GameMode is available under the terms of the BSD 3-Clause License (Revised)