Recent builds have been breaking due to the following error: `/post_build.sh: line 2: npm: command not found`. I’m not entirely sure this is the fix, but it looks like this `latest` tag is now resolving to `3.7.4-buster` (https://hub.docker.com/_/python). Debian Buster got released 2 weeks ago. It feels safer to have a pinned dependency, and Stretch is probably what it was resolving to before.
- Changes the user's email from `@myproject.com` to `@example.com`. myproject.com points to a real website, it feels better to use a domain that's definitely meant as a placeholder.
- Changes the password to `changeme`, matching the credentials used for https://github.com/wagtail/bakerydemo.
Running `npm install` without `--no-save` can introduce spurious changes to package-lock.json due to differences in platform / node version, and these have been known to accidentally sneak into people's PRs. `npm install` without `--no-save` should only be used when actively updating node dependencies in package.json.
