use python 3.6

Author: chenxsan

.github/workflows/build.yml

@@ -37,7 +37,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        python-version: [3.8]
+        python-version: [3.6]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2
@@ -48,6 +48,6 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+          pip install -r requirements.txt
 
       - run: cp .proselintrc ~/ && proselint src/content