Update setup.py for Python 3.9

setup.py

@@ -19,9 +19,9 @@ import sys
 from setuptools import setup, find_packages
 from setuptools.command.test import test as TestCommand
 
-# we only support Python 3 version >= 3.5.3
-if len(sys.argv) >= 2 and sys.argv[1] == "install" and sys.version_info < (3, 5, 3):
-    raise SystemExit("Python 3.5.3 or higher is required")
+# we only support Python 3 version >= 3.6
+if len(sys.argv) >= 2 and sys.argv[1] == "install" and sys.version_info < (3, 6, 0):
+    raise SystemExit("Python 3.6 or higher is required")
 
 
 class PyTest(TestCommand):
@@ -78,6 +78,7 @@ setup(
         "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",
     ],
 )