Duration.toNow() bugs out on certain timestamps or Date objects

[Dolliwyx]

Describe the issue

When Duration#toNow is used on Date objects or timestamps earlier than Date.now(), it returns seconds always.

Code or steps to reproduce

1. Put a timestamp higher than Date.now() on the first parameter of Duration#toNow()

Expected an actual behaviour

Return the actual Duration, returned seconds instead.

Further details

• discord.js version: master branch; commit: 745669a
• node.js version: 10.0.0
• Klasa version: master branch; commit: f58681d
• I have modified core files.
• I have tested the issue on latest master. Commit hash: