There is a missing import for MinecraftServer in JoinIslandCommand.

Introduced in 8aedf1b. Not present in the 1.10.2 port due to this change.

Related: #32

Oh I think I know why this happened, the person who did the PR edited it on GitHub so it didn't add the import. Thanks for letting me know about this.

I should have noticed it before merging, but I was in a rush and let it slip past.