Update scalastyle to allow 2021 in the copyright notice (#396)

scalastyle-config.xml

@@ -92,7 +92,7 @@ This file is divided into 3 sections:
  */
 
 \E)?\Q/*
- * Copyright (2020) The Hyperspace Project Authors.
+ * Copyright (\E(?:2020|2021)\Q) The Hyperspace Project Authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.