Add py38 package metadata

Change-Id: I7e4af300317972767487593a92c3522777e2f628
diff --git a/setup.cfg b/setup.cfg
index 544ea90..144569f 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -16,6 +16,8 @@
     Programming Language :: Python
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
 
 [files]
 packages =