Fixed GetReactionUsersAsync that was not using limit and afterUserId arguments. (#1017)

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -626,7 +626,7 @@ namespace Discord.API
             ulong afterUserId = args.AfterUserId.GetValueOrDefault(0);
 
             var ids = new BucketIds(channelId: channelId);
-            Expression<Func<string>> endpoint = () => $"channels/{channelId}/messages/{messageId}/reactions/{emoji}";
+            Expression<Func<string>> endpoint = () => $"channels/{channelId}/messages/{messageId}/reactions/{emoji}?limit={limit}&after={afterUserId}";
             return await SendAsync<IReadOnlyCollection<User>>("GET", endpoint, ids, options: options).ConfigureAwait(false);
         }
         public async Task AckMessageAsync(ulong channelId, ulong messageId, RequestOptions options = null)