Removing timezone to enable escaping

Hi All-
There is an issue here related to #219 where PyMySQL should strip the timezone from the datetime before inserting. Right now it is failing on the insert, since mysql doesn't take timezone info.

Thanks!
https://docs.python.org/3/library/datetime.html#datetime.date.replace
https://docs.python.org/3/library/datetime.html#datetime.datetime.replace