datasette publish Dockerfile should use python:3.6-slim-stretch

[simonw]

Right now the Dockerfile generated by datasette package and datasette publish uses this:

datasette/datasette/utils.py

Line 269 in b0a95da

FROM python:3

This appears to result in a SQLite version of 3.8.7.1 - https://parlgov.datasettes.com/-/versions

    "sqlite": {
        "extensions": {},
        "fts_versions": [
            "FTS4",
            "FTS3"
        ],
        "version": "3.8.7.1"
    }

Meanwhile, https://fivethirtyeight.datasettes.com/-/versions is deployed with this Dockerfile https://github.com/simonw/fivethirtyeight-datasette/blob/0849901cae06e957fe04892cd4033bdcd1fcf966/Dockerfile which uses FROM python:3.6-slim-stretch and results in the following version report:

    "sqlite": {
        "extensions": {
            "json1": null
        },
        "fts_versions": [
            "FTS5",
            "FTS4",
            "FTS3"
        ],
        "version": "3.16.2"
    }

So not only do we get a more recent SQLite (including https://www.sqlite.org/rowvalue.html added in 3.15) but we also get FTS5 and json1 as well.

Refs #191

[simonw]

I fixed this in b18e451