ConcurrencyException reports an incorrect expected revision number. #61

if (firstEvent.EventNumber - 1 != streams[streamId].Count)
{
    throw new ConcurrencyException($"Concurrency conflict when appending to stream {streamId}. Expected revision {firstEvent.EventNumber} : Actual revision {streams[streamId].Count}");
}

if (firstEvent.EventNumber != streams[streamId].Count + 1)
{
    throw new ConcurrencyException($"Concurrency conflict when appending to stream {streamId}. Expected revision {firstEvent.EventNumber} : Actual revision {streams[streamId].Count + 1}");
}