Update License field to SPDX

- Additionally, correct the License field for the -doc subpackage to
  reflect its dual license.

festival-freebsoft-utils.spec

@@ -5,7 +5,9 @@ Summary:        Utilities that enhance Festival with some useful features
 
 BuildArch:      noarch
 
-License:        GPLv2+
+# Note that the documentation is dual-licensed; see the License field for the
+# -doc subpackage.
+License:        GPL-2.0-or-later
 URL:            https://www.freebsoft.org/festival-freebsoft-utils
 Source0:        https://freebsoft.org/pub/projects/%{name}/%{name}-%{version}.tar.gz
 
@@ -51,6 +53,8 @@ Key festival-freebsoft-utils features are:
 %package doc
 Summary:        Documentation for festival-freebsoft-utils
 
+License:        GPL-2.0-or-later OR GFDL-1.2-no-invariants-or-later
+
 BuildRequires:  make
 BuildRequires:  texinfo-tex
 BuildRequires:  tex(latex)