fix(demo): correct DemoView route

Fixes #4

Author: javier-godoy

src/test/java/com/flowingcode/vaadin/addons/errorwindow/DemoView.java

@@ -24,7 +24,7 @@
 import com.vaadin.flow.component.orderedlayout.VerticalLayout;
 import com.vaadin.flow.router.Route;
 
-@Route()
+@Route("")
 public class DemoView extends VerticalLayout {
 
 	public DemoView() {