nextDelay method
Gets the next delay and increases the backoff
Implementation
Duration nextDelay() {
final delay = _currentDelay;
// Double the delay for next time, but don't exceed max
_currentDelay = Duration(milliseconds: _currentDelay.inMilliseconds * 2);
if (_currentDelay > _maxDelay) {
_currentDelay = _maxDelay;
}
return delay;
}