React to DependencyInjection changes (#869)

src/Microsoft.AspNetCore.Hosting.Abstractions/HostingAbstractionsWebHostBuilderExtensions.cs

@@ -77,7 +77,8 @@ namespace Microsoft.AspNetCore.Hosting
             {
                 // It would be nicer if this was transient but we need to pass in the
                 // factory instance directly
-                services.AddSingleton(server);
+                // Registering as factory so server gets disposed along with a WebHost
+                services.AddSingleton(provider => server);
             });
         }