PM-4.0 support for PiggyAuctions

[Ifera]

Please make sure your issue complies with these guidelines:

• • [X] Use same formatting
• • [X] Changes must have been tested on PMMP.
• • [X] Unless it is a minor code modification, you must use an IDE.
• • [X] Have a detailed title.

What does the PR change?

Adds support for PM API 4.0.

Testing Environment

• PocketMine-MP: 4.0.0
• PHP: 7.3
• Server OS: Windows

Extra Information

N/A

[ZiteDesigns]

please approve this asap!