Fix for commands stopping working after logout

https://github.com/BentoBoxWorld/bentobox/issues/239

The player must be removed from the User cache on logout because the
player object becomes stale and if the player logs in again, they will
still have the old player object.

src/main/java/world/bentobox/bentobox/listeners/JoinLeaveListener.java

@@ -59,5 +59,6 @@ public class JoinLeaveListener implements Listener {
     @EventHandler(priority = EventPriority.NORMAL)
     public void onPlayerQuit(final PlayerQuitEvent event) {
         players.save(event.getPlayer().getUniqueId());
+        User.removePlayer(event.getPlayer());
     }
 }