Add Python 3.7, 3.8, and 3.9 to setup classifiers

Author: Harmon758

setup.py

@@ -41,6 +41,9 @@
         "Programming Language :: Python :: 3.4",
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3 :: Only",
     ],
     long_description=long_description,