Drop to python3.6 as lowest supported version

.github/workflows/release.yaml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python: [3.8]
+        python: [3.6]
 
     steps:
       - uses: actions/checkout@v2

.github/workflows/sphinx.yaml

@@ -14,7 +14,7 @@ jobs:
       - name: Install Python
         uses: actions/setup-python@v1
         with:
-          python-version: 3.8
+          python-version: 3.6
       - name: Install Tox and any other packages
         run: pip install tox
       - name: Build Sphinx docs

.github/workflows/test.yaml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python: [3.8]
+        python: [3.6, 3.7, 3.8]
 
     steps:
       - uses: actions/checkout@v2

setup.py

@@ -7,7 +7,7 @@ from setuptools import setup  # type: ignore
 setup(
     use_scm_version=True,
     setup_requires=['setuptools_scm'],
-    python_requires='>=3.8, <4',
+    python_requires='>=3.6, <4',
     install_requires=[
         'aiokafka==0.6.0',
         'asyncpg==0.21.0',