Fix copyright text in Go source files

Apparently the space after is important or Go will consider the
copyright comments as package documentation.

See: #6

main.go

@@ -1,5 +1,6 @@
 // Copyright 2021 Clayton Craft <clayton@craftyguy.net>
 // SPDX-License-Identifier: GPL-3.0-or-later
+
 package main
 
 import (