replace license with spdx.org variant

OBS-URL: https://build.opensuse.org/package/show/openSUSE:Factory/tar?expand=0&rev=37

tar.spec

@@ -22,7 +22,7 @@
 Name:           tar
 Version:        1.26
 Release:        1
-License:        GPLv3+
+License:        GPL-3.0+
 Summary:        GNU implementation of tar ((t)ape (ar)chiver)
 Url:            http://www.gnu.org/software/tar/
 Group:          System/Base
@@ -49,7 +49,7 @@ provided by tar you have to also install the 'dump' or the 'star'
 package.
 
 %package backup-scripts
-License:        GPLv3+
+License:        GPL-3.0+
 Summary:        Backup scripts
 Group:          Productivity/Archiving/Backup
 Requires:       %{name} = %{version}