Fix: documentation

[RichDom2185]

Based on the changes to the example in #138, it seems that the intended use case is still to specify the interval in minutes:

• guardian_db/lib/guardian/db.ex

  Lines 35 to 36 in 5bcc4d5

  	* `sweep_interval` - The interval between db sweeps to remove old tokens.
  	Default 60 (minutes).

• guardian_db/lib/guardian/db.ex

  Lines 44 to 46 in 5bcc4d5

  	```elixir
  	worker(Guardian.DB.Sweeper, [interval: 60])
  	```

But in the refactoring done in #130, the interval option is passed directly into the worker, without going through the minute-to-millisecond conversion.

This PR restores the original behavior, and also updates the outdated example in the README following the refactor.

If we don't want to keep this minute-to-ms behavior, the alternative is to update the examples accordingly; in that case, this PR could be the starting point for the discussion.

[RichDom2185]

• guardian_db/lib/guardian/db.ex

  Lines 35 to 36 in 5bcc4d5

  	* `sweep_interval` - The interval between db sweeps to remove old tokens.
  	Default 60 (minutes).

Regarding this, I also feel that the v3.0.0 Breaking Changes esction in CHANGELOG.md should be updated to include the fact that the sweep_interval option now does nothing, following #130.

In the same vein, these lines should be removed from lib/guardian/db.ex.

Let me know what you think of these and I'll make the changes accordingly.

[yordis]

hey there, ideally, we take ms and avoid any conversion

[RichDom2185]

hey there, ideally, we take ms and avoid any conversion

Ok, in that case, shall we update the documentation instead? I've updated the PR accordingly.