Deprecation warning

[FM-96]

When using the CLI tool it prints this deprecation warning:

(node:38084) DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.

This does not impact functionality, but it is rather unsightly, and would be an easy fix (just add the specified option).

[mariuspopaadrian]

In mongodb 4.x, those options were removed https://github.com/mongodb/node-mongodb-native/blob/4.0/docs/CHANGES_4.0.0.md

Automattic/mongoose#10500 (comment)