Update Python versions in CI

Author: mwcraig

.github/workflows/build.yml

@@ -9,7 +9,7 @@ jobs:
       max-parallel: 4
       fail-fast: false
       matrix:
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.7, 3.8, 3.9]
         platform: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.platform }}
 

.github/workflows/upload_pypi.yml

@@ -11,7 +11,7 @@ jobs:
       max-parallel: 4
       fail-fast: false
       matrix:
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.7, 3.8, 3.9]
         platform: [macos-latest, windows-latest]  # No wheels on linux yet
     runs-on: ${{ matrix.platform }}