fix(v2.15.6, #507): correct handling for symbols array in rolling window tickers endpoint

[tiagosiebler]

Summary

Fixes how the "symbols" array parameter is built into a request for the rolling window ticker endpoint:

    const rollingTicker = await client.getRollingWindowTicker({
      symbols: ['BTCUSDT', 'ETHUSDT'],
      windowSize: '5m',
      type: 'MINI',
    });
    console.log('getRollingWindowTicker', rollingTicker);

Fixes #507.

Additional Information