Remove 3.6 from CI runs

Author: joshmoore

.github/workflows/ci-linux.yaml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.6", "3.7", "3.8", "3.9"]
+        python-version: ["3.7", "3.8", "3.9"]
         os: [ubuntu-18.04, ubuntu-20.04]
 
     steps:

.github/workflows/ci-osx.yaml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.6", "3.7", "3.8", "3.9"]
+        python-version: ["3.7", "3.8", "3.9"]
 
     steps:
       - name: Checkout source

.github/workflows/ci-windows.yaml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.6", "3.7", "3.8", "3.9"]
+        python-version: ["3.7", "3.8", "3.9"]
 
     steps:
       - name: Checkout source