fix binance ticker websocket with symbol (#794)

Author: szmcdull

src/ExchangeSharp/API/Exchanges/BinanceGroup/BinanceGroupCommon.cs

@@ -269,11 +269,21 @@ protected override async Task<IWebSocket> OnGetTickersWebSocketAsync(Action<IRea
 JToken token = JToken.Parse(msg.ToStringFromUTF8());
 List<KeyValuePair<string, ExchangeTicker>> tickerList = new List<KeyValuePair<string, ExchangeTicker>>();
 ExchangeTicker ticker;
-foreach (JToken childToken in token["data"])
+
+// if it is the tickers stream, data will be an array, else it is an direct item.
+var data = token["data"];
+if (data is JArray)
+foreach (JToken childToken in data)
+{
+ticker = await ParseTickerWebSocketAsync(childToken);
+tickerList.Add(new KeyValuePair<string, ExchangeTicker>(ticker.MarketSymbol, ticker));
+}
+else
 {
-ticker = await ParseTickerWebSocketAsync(childToken);
+ticker = await ParseTickerWebSocketAsync(data);
 tickerList.Add(new KeyValuePair<string, ExchangeTicker>(ticker.MarketSymbol, ticker));
 }
+
 if (tickerList.Count != 0)
 {
 callback(tickerList);