build: drop Python 3.6 and 3.7 support

Author: mbdevpl

README.rst

@@ -436,7 +436,7 @@ using version-query without any issues.
 Requirements
 ============
 
-Python version 3.6 or later.
+Python version 3.8 or later.
 
 Python libraries as specified in `<requirements.txt>`_.
 

setup.py

@@ -20,9 +20,9 @@ class Package(setup_boilerplate.Package):
         'Operating System :: MacOS :: MacOS X',
         'Operating System :: Microsoft :: Windows',
         'Operating System :: POSIX :: Linux',
-        'Programming Language :: Python :: 3.6',
-        'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
+        'Programming Language :: Python :: 3.10',
         'Programming Language :: Python :: 3 :: Only',
         'Topic :: Software Development :: Version Control',
         'Topic :: Software Development :: Version Control :: Git',