Fix date field less than 1900

[megies]

This fixes a bug when writing to date fields with values of before 1900AD. datetime.datetime.strftime() raises an exception when used with dates earlier than 1900AD but it's trivial to just use plain string formatting instead.

[karimbahgat]

I recently came across this datetime limitation in another setting, should be useful for a lot of historical data. Thanks 👍