20.0.0 before 2020 is even over (#968)

diff --git a/setup.py b/setup.py
index 08769d2..fbd6571 100755
--- a/setup.py
+++ b/setup.py
@@ -83,6 +83,7 @@
             "Programming Language :: Python :: 3.6",
             "Programming Language :: Python :: 3.7",
             "Programming Language :: Python :: 3.8",
+            "Programming Language :: Python :: 3.9",
             "Programming Language :: Python :: Implementation :: CPython",
             "Programming Language :: Python :: Implementation :: PyPy",
             "Topic :: Security :: Cryptography",