Fix WorldGuard again

[ghost]

Re-adds methods in Futures without an executor argument that were removed in Guava 26.0

Additional Comments

I haven’t tested but it should work.

Checklist:

• [x] I have reviewed my code thoroughly.
• [ ] I have tested my code.
• [x] My changes generate no new warnings

@Lucaskyy

[Sculas]

You probably already saw, but anyway; checks failed :p Thanks for the PR though! I'll merge it once checks succeed :)

[Sculas]

Thank you!