Fix router for 3.1 preview1

Author: galvesribeiro

test/Blazor.Extensions.Logging.Test/App.razor

@@ -1,5 +1,14 @@
-<!--
-    Configuring this here is temporary. Later we'll move the app config
-    into Program.cs, and it won't be necessary to specify AppAssembly.
--->
-<Router AppAssembly="typeof(Program).Assembly" />
+<!--
+    Configuring this here is temporary. Later we'll move the app config
+    into Program.cs, and it won't be necessary to specify AppAssembly.
+-->
+<Router AppAssembly="typeof(Program).Assembly" >
+    <Found Context="routeData">
+        <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)" />
+    </Found>
+    <NotFound>
+        <LayoutView Layout="@typeof(MainLayout)">
+            <p>Sorry, there's nothing at this address.</p>
+        </LayoutView>
+    </NotFound>
+</Router>