Added trailing slash to /Error/ path

Added a missing trailing `/` to the `UseStatusCodePagesWithReExecute()` registration. That isn't strictly necessary, but it helps avoid an otherwise unnecessary potential redirect to the canonical URL from the `[ValidateTopic]` attribute.

Author: JeremyCaney

OnTopic.AspNetCore.Mvc.Host/Program.cs

@@ -54,7 +54,7 @@
 | Configure: Error Pages
 \-----------------------------------------------------------------------------------------------------------------------------*/
 if (!app.Environment.IsDevelopment()) {
-  app.UseStatusCodePagesWithReExecute("/Error/{0}");
+  app.UseStatusCodePagesWithReExecute("/Error/{0}/");
   app.UseExceptionHandler("/Error/500/");
   // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
   app.UseHsts();

OnTopic.AspNetCore.Mvc.IntegrationTests.Host/Startup.cs

@@ -82,7 +82,7 @@ public static void Configure(IApplicationBuilder app) {
       | Configure: Error Pages
       \-----------------------------------------------------------------------------------------------------------------------*/
       app.UseDeveloperExceptionPage();
-      app.UseStatusCodePagesWithReExecute("/Error/{0}");
+      app.UseStatusCodePagesWithReExecute("/Error/{0}/");
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Configure: Server defaults