FileUpload sample is Returning abstract class FileResult

[v-paulino]

Hi there

I was checking the code sample FileUpload and just realized that the ActionResult instance type is FileResult that currently is abstract.
FileResult: https://docs.microsoft.com/en-us/dotnet/api/system.web.mvc.fileresult?view=aspnet-mvc-5.2

This needs to be updated to one of the inherit types i guess:
System.Web.Mvc.FileContentResult
System.Web.Mvc.FilePathResult
System.Web.Mvc.FileStreamResult