`bin/manage_users` drops deprecation warning for future node-postgres versions

[bonanza123]

Currently, I get the following warning when using the bin/manage_users script:

(node:78) DeprecationWarning: Using the automatically created return value from client.query as an event emitter is deprecated and will be removed in pg@7.0. Please see the upgrade guide at https://node-postgres.com/guides/upgrading
Using password from commandline...

[SISheogorath]

This has a simple reason: It uses the sequelize version of CodiMD which is currently still version 3.

It'll disappear when we switch to version 4: #873