*: 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>

shell/shell_common.h

@@ -14,7 +14,7 @@
  * Copyright (c) 2010 Denys Vlasenko
  * Split from ash.c
  *
- * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  */
 #ifndef SHELL_COMMON_H
 #define SHELL_COMMON_H 1