Put python-dotenv in the packages section of the Pipfile instead of the dev-packages section

[liammulh]

On the prod server, we pipenv sync. This only installs the dependencies in the packages section. It ignores the dev-packages section because those are supposed to be only used for development, i.e. not needed in prod. To make sure we have python-dotenv in prod, it needs to be in the packages section.