Fix ConnectionListener for player leave

src/de/steamwar/misslewars/listener/ConnectionListener.java

@@ -22,6 +22,7 @@ package de.steamwar.misslewars.listener;
 import de.steamwar.misslewars.FightState;
 import de.steamwar.misslewars.MWTeam;
 import de.steamwar.misslewars.MissileWars;
+import org.bukkit.Bukkit;
 import org.bukkit.GameMode;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
@@ -47,6 +48,10 @@ public class ConnectionListener extends BasicListener{
 	public void onLeave(PlayerQuitEvent e) {
 		MWTeam.removeInvitations(e.getPlayer());
 		MissileWars.leave(e.getPlayer());
+
+		if (Bukkit.getOnlinePlayers().isEmpty()) {
+			Bukkit.shutdown();
+		}
 	}
 
 }