Add Python 3.8 classifier to setup.cfg

setup.cfg

@@ -20,6 +20,7 @@ classifiers =
     Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
     Programming Language :: Python :: Implementation :: CPython
     Topic :: Games/Entertainment
     Topic :: Multimedia