Test with multiple Python versions

In particular, runners and Node.js seems to be failing with Python 2.
We'd better test those to see if they ever break on us.

.github/workflows/main.yml

@@ -16,6 +16,13 @@ jobs:
     runs-on: windows-latest
     strategy:
       fail-fast: false
+      matrix:
+        python-version:
+          - '2.7'
+          - '3.5'
+          - '3.6'
+          - '3.7'
+          - '3.8'
     steps:
       - name: Check out source code
         uses: actions/checkout@v1

.github/workflows/release.yml

@@ -14,6 +14,13 @@ jobs:
     runs-on: windows-latest
     strategy:
       fail-fast: false
+      matrix:
+        python-version:
+          - '2.7'
+          - '3.5'
+          - '3.6'
+          - '3.7'
+          - '3.8'
     steps:
       - name: Setup Developer Command Prompt
         uses: ilammy/msvc-dev-cmd@v1