Use JsonConvert for API keys list (#7256)

Author: Scott Bommarito

src/NuGetGallery/Views/Users/ApiKeys.cshtml

@@ -1,4 +1,5 @@
-@model ApiKeyListViewModel
+@using Newtonsoft.Json
+@model ApiKeyListViewModel
 @using NuGetGallery.Authentication
 @{
     ViewBag.Title = "API Keys";
@@ -463,7 +464,7 @@
 
 @section bottomScripts {
     <script type="text/javascript">
-        var initialData = @Html.Raw(Json.Encode(new
+        var initialData = @Html.Raw(JsonConvert.SerializeObject(new
                      {
                          ApiKeys = Model.ApiKeys,
                          PackageOwners = Model.PackageOwners,