Fixed warning

src/gui/MainWindow.java

@@ -4,6 +4,8 @@ import javax.swing.JFrame;
 
 public class MainWindow extends JFrame{
 
+	private static final long serialVersionUID = 13L;
+
 	public MainWindow(){
 		JFrame fenetre = new JFrame();
 		fenetre.setTitle("Client");

src/gui/Parameters.java

@@ -11,6 +11,7 @@ import java.awt.GridLayout;
 
 public class Parameters extends JPanel{
 
+	private static final long serialVersionUID = 13L;
 	private JLabel label1, label2, label3, label4, label5;
 	private JTextField field1, field2, field3, field4;
 	private JButton connectButton;

src/gui/downloadSelection.java

@@ -12,6 +12,7 @@ import java.awt.GridLayout;
 
 public class downloadSelection extends JPanel {
 
+	private static final long serialVersionUID = 13L;
 	private String[] listFilesToDownload;
 	private JList<String> list1;
 	private JLabel label1;