*: 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/applets/usage_pod.c b/applets/usage_pod.c
index 85a2a8e..da0baef 100644
--- a/applets/usage_pod.c
+++ b/applets/usage_pod.c
@@ -2,7 +2,7 @@
 /*
  * Copyright (C) 2009 Denys Vlasenko.
  *
- * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ * Licensed under GPLv2, see file LICENSE in this source tree.
  */
 #include <unistd.h>
 #include <stdint.h>