@Override
    public Retryer clone() {
      return new Default(period, maxPeriod, maxAttempts);
    }
Calculates the time interval to a retry attempt.<br>
The interval increases exponentially with each attempt, at a rate of nextInterval *= 1.5
(where 1.5 is the backoff factor), to the maximum interval.

@return time in milliseconds from now until the next attempt.
core/src/main/java/feign/Retryer.java