*: 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/archival/libunarchive/decompress_unxz.c b/archival/libunarchive/decompress_unxz.c
index 721acd9..faba9ca 100644
--- a/archival/libunarchive/decompress_unxz.c
+++ b/archival/libunarchive/decompress_unxz.c
@@ -7,7 +7,7 @@
  *
  * This file is:
  * Copyright (C) 2010 Denys Vlasenko <vda.linux@googlemail.com>
- * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ * Licensed under GPLv2, see file LICENSE in this source tree.
  */
 #include "libbb.h"
 #include "unarchive.h"