Drop testing on Python 3.6

Author: takluyver

appveyor.yml

@@ -6,7 +6,6 @@ image: Visual Studio 2019
 # environment variables
 environment:
   matrix:
-    - PYTHON: "C:\\Python36-x64"
     - PYTHON: "C:\\Python37-x64"
     - PYTHON: "C:\\Python38-x64"
     - PYTHON: "C:\\Python39-x64"

setup.py

@@ -27,7 +27,7 @@
         'ipykernel',
         'coverage',
     ],
-    python_requires='>=3.6, <4',
+    python_requires='>=3.7, <4',
     classifiers = [
         'Framework :: IPython',
         'Framework :: Pytest',