python: update setup.py to use a SPDX license expression

python/setup.py.in

@@ -27,14 +27,13 @@ setup(name="opendht",
       description="Python wrapper for OpenDHT",
       url='https://github.com/savoirfairelinux/opendht',
       author="Adrien Béraud, Guillaume Roguez, Simon Désaulniers",
-      license="GPLv3",
+      license="GPL-3.0-or-later",
       classifiers=[
           'Development Status :: 5 - Production/Stable',
           'Intended Audience :: Developers',
           'Topic :: Software Development :: Libraries :: Python Modules',
           'Topic :: System :: Distributed Computing',
           'Topic :: System :: Networking',
-          'License :: OSI Approved :: GNU General Public License v3 or later (GPLv3+)',
           'Programming Language :: Python :: 3',
           'Programming Language :: Python :: 3.7',
       ],