chore(demo): update error message and remove notification

Author: javier-godoy

src/test/java/com/flowingcode/vaadin/addons/xterm/XtermDemoView.java

@@ -24,7 +24,6 @@
 import com.flowingcode.vaadin.addons.xterm.ITerminalClipboard.UseSystemClipboard;
 import com.flowingcode.vaadin.addons.xterm.ITerminalOptions.BellStyle;
 import com.flowingcode.vaadin.addons.xterm.ITerminalOptions.CursorStyle;
-import com.vaadin.flow.component.notification.Notification;
 import com.vaadin.flow.component.orderedlayout.VerticalLayout;
 import com.vaadin.flow.router.Route;
 import java.time.LocalDate;
@@ -97,9 +96,8 @@ public XtermDemoView() {
               break;
             default:
               if (!ev.getLine().trim().isEmpty()) {
-                xterm.writeln("Bad command");
+                xterm.writeln("Unknown command: " + line[0]);
               }
-              Notification.show(ev.getLine());
           }
         });