Use modern HttpClient

(cherry picked from commit 402f8b296f17bf161824ec5ff40d67d036d00d94)

src/NzbDrone.Common/Http/HttpRequest.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Net;
+using System.Net.Http;
 using System.Text;
 using NzbDrone.Common.EnvironmentInfo;
 using NzbDrone.Common.Extensions;
@@ -12,6 +13,7 @@ namespace NzbDrone.Common.Http
     {
         public HttpRequest(string url, HttpAccept httpAccept = null)
         {
+            Method = HttpMethod.Get;
             Url = new HttpUri(url);
             Headers = new HttpHeader();
             AllowAutoRedirect = true;