*: 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>

docs/new-applet-HOWTO.txt

@@ -36,7 +36,7 @@ For a new applet mu, here is the code that would go in mu.c:
  *
  * Copyright (C) [YEAR] by [YOUR NAME] <YOUR EMAIL>
  *
- * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ * Licensed under GPLv2, see file LICENSE in this source tree.
  */
 
 #include "libbb.h"