fix warning serial version

src/gui/DownloadFileGUI.java

@@ -27,11 +27,14 @@ import java.net.SocketException;
 import javax.swing.JFrame;
 import javax.swing.JPanel;
 
+
 public class DownloadFileGUI extends JPanel{
 
 	private String fileToDownload;
 	private ClientManagement clientManagement;
 	private Logger logger;
+	private static final long serialVersionUID = 13L;
+
 
 	public DownloadFileGUI(String fileToDownload, ClientManagement clientManagement, Logger logger){
 		this.fileToDownload = fileToDownload;