Update django-localflavor and pin to specific versions in pyproject.toml

Ghost User
2020-02-05T12:24:12+01:00

This MR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [django-localflavor](https://github.com/django/django-localflavor) | dev-dependencies | major | `~2.1` -> `latest git revision` |

I do not want to wait for a release, the code does seem stable as is. And this is required for django 3.0.

This MR also pins the versions in pyproject.yml so that renovate can update all, since apparently it's missing stuff.