Downgrade Python version to 3.8

Why these changes are being introduced:
Our current EC2 instance (where this app will be run for now) runs on
Ubuntu 18.04, which can't handle Python 3.9. So we're reverting to 3.8
until deployment plans change.

How this addresses that need:
* Updates Pipfile and Pipfile.lock to require Python 3.8
* Also updates the Python version used in Github Actions workflows for
  consistency

Author: hakbailey

.github/workflows/tests.yml

@@ -11,7 +11,7 @@ jobs:
       - name: Setup python
         uses: actions/setup-python@v2
         with:
-          python-version: '3.9'
+          python-version: '3.8'
           architecture: x64
       - name: Install
         run: |
@@ -27,11 +27,11 @@ jobs:
       - name: Setup python
         uses: actions/setup-python@v2
         with:
-          python-version: '3.9'
+          python-version: '3.8'
           architecture: x64
       - name: Install
         run: |
           python -m pip install --upgrade pip pipenv
           pipenv install --dev
       - name: Linting
-        run: make lint
+        run: make lint

Pipfile

@@ -23,7 +23,7 @@ moto = {extras = ["s3"], version = "*"}
 freezegun = "*"
 
 [requires]
-python_version = "3.9"
+python_version = "3.8"
 
 [scripts]
 llama = "python -c \"from llama.cli import cli; cli()\""