Relax Py3 requirements to >= 3.6

Unfortunately, CentOS 8 users must rely on Py3.6

Author: alvarolopez

setup.cfg

@@ -15,7 +15,7 @@ project_urls =
 license = Apache-2
 license_file = LICENSE
 
-python_requires = >=3.7
+python_requires = >=3.6
 
 classifier =
     Development Status :: 5 - Production/Stable
@@ -27,6 +27,7 @@ classifier =
     Operating System :: POSIX :: Linux
     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