[trivial] add python 3.9 in classifier

Change-Id: Id6c16e3bb6157966fa59015db1a7da58bf0e479d
diff --git a/setup.cfg b/setup.cfg
index 824127d..a5cf426 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -17,6 +17,7 @@
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
 
 [files]
 packages =