Fix callback command not working (#1464)

Broken in 2016d14#diff-1217e64751ab6522195a858620cceeb4f2d2b6506c36dd4e396726ad3e7ef0cb

Author: riku6460

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -253,7 +253,7 @@ void start() {
         commandManager.metaBuilder(callbackCommand)
             .plugin(VelocityVirtualPlugin.INSTANCE)
             .build(),
-        velocityParentCommand
+        callbackCommand
     );
     final BrigadierCommand serverCommand = ServerCommand.create(this);
     commandManager.register(