fix classifier

Author: slhck

setup.py

@@ -48,7 +48,7 @@
         "Topic :: Multimedia :: Sound/Audio",
         "Topic :: Multimedia :: Sound/Audio :: Analysis",
         "Topic :: Multimedia :: Sound/Audio :: Conversion",
-        "MIT",
+        "License :: OSI Approved :: MIT License",
         "Natural Language :: English",
         "Programming Language :: Python :: 3",
         "Programming Language :: Python :: 3.9",