Migrate to SPDX license

This is a part of https://fedoraproject.org/wiki/Changes/SPDX_Licenses_Phase_3

python-urwid.spec

@@ -7,7 +7,8 @@ Version:       2.4.6
 Release:       %autorelease
 Summary:       Console user interface library
 
-License:       LGPLv2+
+# examples/twisted_serve_ssh.py is MIT
+License:       LGPL-2.1-or-later AND MIT
 URL:           http://excess.org/urwid/
 Source0:       %{pypi_source urwid}