fixed the timestamp variables calculation

fix for both https://github.com/itguy51/ep_signature/issues/7 and https://github.com/itguy51/ep_signature/issues/8

There were several problems:
* getMonth returns values in the range of 0..11
* getDay is not the day of the month but the day of the week (getDate is correct)
* you used %m% for minutes and month. I changed this, so that YMD are for year month date, and "m" is for minutes.