package/libutempter: fix license information

According to the source file:

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/libutempter/libutempter.mk

@@ -7,7 +7,7 @@
 LIBUTEMPTER_VERSION = 1.2.1
 LIBUTEMPTER_SITE = ftp.altlinux.org/pub/people/ldv/utempter
 LIBUTEMPTER_INSTALL_STAGING = YES
-LIBUTEMPTER_LICENSE = LGPL-2.1
+LIBUTEMPTER_LICENSE = LGPL-2.1+
 LIBUTEMPTER_LICENSE_FILES = COPYING
 
 define LIBUTEMPTER_BUILD_CMDS