Fixes UmbracoIntegrationTest Mapping flag and missing using in Startup

src/Umbraco.Web.UI.NetCore/Startup.cs

@@ -4,6 +4,7 @@ using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
+using Umbraco.Core.DependencyInjection;
 using Umbraco.Extensions;
 using Umbraco.Web.BackOffice.DependencyInjection;
 using Umbraco.Web.BackOffice.Security;