fix pypi license classifier

Author: letmaik

setup.py

@@ -121,7 +121,7 @@ def build_extensions(self):
         'Development Status :: 4 - Beta',
         'Intended Audience :: Developers',
         'Natural Language :: English',
-        'OSI Approved :: GNU General Public License v2 (GPLv2)',
+        'License :: OSI Approved :: GNU General Public License v2 (GPLv2)',
         'Programming Language :: Python :: 3',
         'Operating System :: Microsoft :: Windows',
         'Topic :: Multimedia :: Graphics',