Add missing "=back" to fix pod2man error.

--- a/rsnapshot-program.pl
+++ b/rsnapshot-program.pl
@@ -6716,6 +6716,8 @@
 
 =back
 
+=back
+
 =head1 USAGE
 
 B<rsnapshot> can be used by any user, but for system-wide backups
