Add py38 package metadata

Change-Id: I57bf025751bc739e4cea7b00c909425718a3feba
diff --git a/setup.cfg b/setup.cfg
index 7d2ca94..3cf22d8 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -20,6 +20,7 @@
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
     Topic :: Internet :: Name Service (DNS)
 
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