Merge pull request #1 from msx752/msx752-patch-1

fix for 'unsupported property on RestNewsChannel'

src/Discord.Net.Rest/Entities/Channels/RestTextChannel.cs

@@ -42,7 +42,8 @@ namespace Discord.Rest
             base.Update(model);
             CategoryId = model.CategoryId;
             Topic = model.Topic.Value;
-            SlowModeInterval = model.SlowMode.Value;
+            if (model.SlowMode.IsSpecified)
+                SlowModeInterval = model.SlowMode.Value;
             IsNsfw = model.Nsfw.GetValueOrDefault();
         }