update python version 3.7 -> 3.8

Author: mrdbourke

.github/workflows/make_docs.yml

@@ -23,7 +23,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
         with:
-          python-version: 3.7
+          python-version: 3.8
       - uses: actions/cache@v2
         with:
           key: ${{ github.ref }}