Remove Python 3.9 classifier from setup.cfg (#243)

Author: adamchainz

setup.cfg

@@ -23,7 +23,6 @@ classifiers =
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
-    Programming Language :: Python :: 3.9
 license_file = LICENSE
 
 [options]