py3: use Python 3.6 to publish capa

.github/workflows/publish.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: '2.7'
+          python-version: '3.6'
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
@@ -27,3 +27,4 @@ jobs:
         run: |
           python setup.py sdist bdist_wheel
           twine upload --skip-existing dist/*
+