*: make GNU licensing statement forms more regular

This change retains "or later" state! No licensing _changes_ here,
only form is adjusted (article, space between "GPL" and "v2" and so on).

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/coreutils/dd.c b/coreutils/dd.c
index 7c1a0c0..aa6f765 100644
--- a/coreutils/dd.c
+++ b/coreutils/dd.c
@@ -5,7 +5,7 @@
  *
  * Copyright (C) 2000,2001  Matt Kraai
  *
- * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  */
 
 #include "libbb.h"