Use python:3.8 base Docker image, refs #629

datasette/utils/__init__.py

@@ -306,7 +306,7 @@ def make_dockerfile(
         install = ["datasette"] + list(install)
 
     return """
-FROM python:3.6
+FROM python:3.8
 COPY . /app
 WORKDIR /app
 {spatialite_extras}

tests/test_publish_cloudrun.py

@@ -128,7 +128,7 @@ def test_publish_cloudrun_plugin_secrets(mock_call, mock_output, mock_which):
             .split("\n====================\n")[0]
             .strip()
         )
-        expected = """FROM python:3.6
+        expected = """FROM python:3.8
 COPY . /app
 WORKDIR /app
 

tests/test_publish_now.py

@@ -138,7 +138,7 @@ def test_publish_now_plugin_secrets(mock_run, mock_which):
             .split("\n====================\n")[0]
             .strip()
         )
-        expected = """FROM python:3.6
+        expected = """FROM python:3.8
 COPY . /app
 WORKDIR /app