Drop support for EOL Python 3.6

Version 3.6 reached its end-of-life phase on 2021-12-23.
According to PEP 494 - https://peps.python.org/pep-0494/

Author: CairX

convcolors/__init__.py

@@ -1,5 +1,3 @@
-# coding: utf8
-
 import math
 
 

setup.cfg

@@ -2,7 +2,7 @@
 testpaths = tests
 
 [tox:tox]
-envlist = py36,py37,py38
+envlist = py37,py38
 
 [testenv]
 deps = pytest

setup.py

@@ -17,15 +17,14 @@
         "License :: OSI Approved :: MIT License",
         "Natural Language :: English",
         "Programming Language :: Python :: 3 :: Only",
-        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3",
         "Topic :: Multimedia :: Graphics :: Graphics Conversion",
         "Topic :: Software Development :: Libraries :: Python Modules",
         "Topic :: Utilities",
     ],
-    python_requires=">=3.6",
+    python_requires=">=3.7",
     keywords="convert colors",
     packages=["convcolors"],
     extras_require={