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.WebSocket/Net/DefaultWebSocketClientProvider.cs

@@ -5,7 +5,6 @@ namespace Discord.Net.WebSockets
 {
     public static class DefaultWebSocketProvider
     {
-#if DEFAULTWEBSOCKET
         public static readonly WebSocketProvider Instance = Create();
 
         public static WebSocketProvider Create(IWebProxy proxy = null)
@@ -22,12 +21,5 @@ namespace Discord.Net.WebSockets
                 }
             };
         }
-#else
-        public static readonly WebSocketProvider Instance = () =>
-        {
-            throw new PlatformNotSupportedException("The default WebSocketProvider is not supported on this platform.\n" +
-                "You must specify a WebSocketProvider or target a runtime supporting .NET Standard 1.3, such as .NET Framework 4.6+.");
-        };
-#endif
     }
-}
+}