*: 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/ar.c b/archival/ar.c
index 1b7b66a..bce62f7 100644
--- a/archival/ar.c
+++ b/archival/ar.c
@@ -6,7 +6,7 @@
  *
  * Based in part on BusyBox tar, Debian dpkg-deb and GNU ar.
  *
- * 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.
  *
  * Archive creation support:
  * Copyright (C) 2010 Nokia Corporation. All rights reserved.