Update classifiers for Python versions

Author: alex

setup.cfg

@@ -16,6 +16,8 @@ classifiers =
     Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
     Development Status :: 5 - Production/Stable
     Operating System :: POSIX
     Operating System :: MacOS :: MacOS X