Only build docs on one python version.

This prevents it from trying to upload twice at the same time.

Author: arokem

.github/workflows/docbuild.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       max-parallel: 4
       matrix:
-        python-version: [3.6, 3.7]
+        python-version: [3.7]
 
     steps:
     - name: Checkout repo