feat(packaging): add support for Python 3.8 (#569)

Release-As: 1.20.0

Closes #568
diff --git a/setup.py b/setup.py
index 1f5c686..6a70fca 100644
--- a/setup.py
+++ b/setup.py
@@ -56,6 +56,7 @@
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
         "Development Status :: 5 - Production/Stable",
         "Intended Audience :: Developers",
         "License :: OSI Approved :: Apache Software License",