update mongo config to prevent deprecation warning

[timmyg]

No description provided.

[tibotiber]

@emirotin any chance to merge this?

[emirotin]

Sorry I've stopped maintaining this project long time ago.
I should actually write about it in the readme and try to find the new maintainer.

This change is technically breaking as it drops support for the old-style configuration. To release it as the new minor version the backward-compat handling of the old-style option would be needed similar to how it's already done.

If you're happy with this change and want it asap you can fork the repo, publish it to npm under your username and switch to that copy of yours.

[tibotiber]

Yes, I realised that based on activity after posting. Thanks for responding nonetheless :). FWIW, I switched to https://github.com/seppevs/migrate-mongo after realising your repo was not maintained. If you feel like giving a direction to people who land on your repo, it's been a good replacement for me.