Minor chat panel size edition

src/main/java/ch/hepia/ui/MainWindowController.java

@@ -178,7 +178,7 @@ public class MainWindowController implements Initializable {
                 Insets.EMPTY)));
         p.setBorder(new Border(new BorderStroke(Color.color(0.6, 0.6, 0.6), BorderStrokeStyle.SOLID, new CornerRadii(5),
                 BorderWidths.DEFAULT)));
-        p.setPrefWidth(315);
+        p.setPrefWidth(312);
         p.setMaxWidth(320);
     }