Drop support for Python 3.6 to match Matplotlib/NEP 29

Author: hugovk

.github/workflows/tests.yml

@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        python-version: ["3.6", "3.7", "3.8", "3.9"]
+        python-version: ["3.7", "3.8", "3.9"]
 
     steps:
       - uses: actions/checkout@v2

appveyor.yml

@@ -5,8 +5,6 @@ image: Visual Studio 2019
 
 environment:
   matrix:
-     - PYTHON: "C:\\Python36"
-     - PYTHON: "C:\\Python36-x64"
      - PYTHON: "C:\\Python37"
      - PYTHON: "C:\\Python37-x64"
      - PYTHON: "C:\\Python38"

setup.py

@@ -9,11 +9,10 @@
       url='https://github.com/matplotlib/cycler',
       platforms='Cross platform (Linux, Mac OSX, Windows)',
       license="BSD",
-      python_requires='>=3.6',
+      python_requires='>=3.7',
       classifiers=['License :: OSI Approved :: BSD License',
                    'Development Status :: 4 - Beta',
                    'Programming Language :: Python :: 3',
-                   'Programming Language :: Python :: 3.6',
                    'Programming Language :: Python :: 3.7',
                    'Programming Language :: Python :: 3.8',
                    'Programming Language :: Python :: 3.9',