Update cmake file with new standard header.

Author: janowagner

cmake/GetGit.cmake

@@ -1,13 +1,7 @@
-# getgit.cmake
-# This script attempts to determine the Git commit ID and writes or updates
-# a "gitrevision.h" file if successful.
-#
-# Authors:
-# Juan Jose Nicola <[email protected]>
-#
-# Copyright:
 # Copyright (C) 2018 Greenbone Networks GmbH
 #
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
 # This program is free software; you can redistribute it and/or
 # modify it under the terms of the GNU General Public License
 # as published by the Free Software Foundation; either version 2
@@ -22,6 +16,9 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 
+# This script attempts to determine the Git commit ID and writes or updates
+# a "gitrevision.h" file if successful.
+
 find_package (Git)
 
 macro (Git_GET_REVISION dir variable)