Adding MIT License classifier (#498)

Author: leszekhanusz

setup.py

@@ -84,6 +84,7 @@
         "Development Status :: 5 - Production/Stable",
         "Intended Audience :: Developers",
         "Topic :: Software Development :: Libraries",
+        "License :: OSI Approved :: MIT License",
         "Programming Language :: Python :: 3",
         "Programming Language :: Python :: 3 :: Only",
         "Programming Language :: Python :: 3.8",