Added programming language classifiers

Added programming language classifiers to specify support for Python minor release versions 3.6, 3.7, 3.8, and 3.9.

Author: emuccino

setup.py

@@ -86,6 +86,10 @@
         'License :: OSI Approved :: BSD License',
         'Programming Language :: Python',
         'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
     ],
     install_requires=[
         'jupyter_client',