Add py38 package metadata

Change-Id: I2fb037a15fadf52f5dd918f80d2ef8c82833c24f
diff --git a/setup.cfg b/setup.cfg
index 3e5d216..d7d3196 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -19,6 +19,7 @@
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
 
 [global]
 setup-hooks =