hey, i added a bit of code to support the log format that express.js generates with its default logger. it is mostly an issue with date and timezone.
you probably don't want to pull it verbatim, as the difference between COMMON_LOG_FORMAT and EXPRESS_LOG_FORMAT is just a removed qualifier for the date.
i also had to change the timezone detection as 'GMT' yields a ValueError and i suppose that is fine as timezone = 0.
thanks for piwik!
adding the new log format sounds good, but I dont really like the other change as it could later hide relevant errors in parsing. please try again if you find better fix