dockerfile: Fix copyright

Signed-off-by: Christopher Crone <[email protected]>

Dockerfile

@@ -1,5 +1,5 @@
 # syntax = docker/dockerfile:experimental
-#   Copyright 2020 The 2020 Docker, Inc.
+#   Copyright 2020 Docker, Inc.
 
 #   Licensed under the Apache License, Version 2.0 (the "License");
 #   you may not use this file except in compliance with the License.