Improve Checkstyle config
^/\*
^ \* The MIT License
^ \*
-^ \* Copyright \(c\) \d{4}(-\d{4})? .+$
+^ \* Copyright \(c\) (2020|\d{4}-2020) .+$
^ \*
^ \* Permission is hereby granted, free of charge, to any person obtaining a copy
^ \* of this software and associated documentation files \(the "Software"\), to deal
