Drop py3.6 support from classifiers (#2602)

Author: seanpmorgan

setup.py

@@ -115,7 +115,6 @@ def has_ext_modules(self):
         "Intended Audience :: Science/Research",
         "License :: OSI Approved :: Apache Software License",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",