Update Dependencies and support NS2.0 builds (#1046)

* Update deps, fix test warnings.

* Support ns2.0

* Fix typo

* Remove ns1.1 support

* Net.Http and Net.Websockets.Client are not needed in ns2.0

* Move to net46 per volt

* Remove ns1.3 constants

src/Discord.Net.Webhook/WebhookClientHelper.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -33,7 +33,6 @@ namespace Discord.Webhook
             var model = await client.ApiClient.CreateWebhookMessageAsync(client.Webhook.Id, args, options: options).ConfigureAwait(false);
             return model.Id;
         }
-#if FILESYSTEM
         public static async Task<ulong> SendFileAsync(DiscordWebhookClient client, string filePath, string text, bool isTTS, 
             IEnumerable<Embed> embeds, string username, string avatarUrl, RequestOptions options)
         {
@@ -41,7 +40,6 @@ namespace Discord.Webhook
             using (var file = File.OpenRead(filePath))
                 return await SendFileAsync(client, file, filename, text, isTTS, embeds, username, avatarUrl, options).ConfigureAwait(false);
         }
-#endif
         public static async Task<ulong> SendFileAsync(DiscordWebhookClient client, Stream stream, string filename, string text, bool isTTS,
             IEnumerable<Embed> embeds, string username, string avatarUrl, RequestOptions options)
         {