Implemented config for asp.net core

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

@@ -5,6 +5,7 @@ using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Umbraco.Web.BackOffice.AspNetCore;
@@ -15,6 +16,7 @@ namespace Umbraco.Web.UI.BackOffice
 {
     public class Startup
     {
+
         // This method gets called by the runtime. Use this method to add services to the container.
         // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
         public void ConfigureServices(IServiceCollection services)