🐛 xlsxwriter: `datetime_to_excel_datetime` import fails

[ollyhensby]

Issue

Import fails due to datetime_to_excel_datetime function in xlsxwriter.utility:

xlsxdatagrid/src/xlsxdatagrid/xlsxdatagrid.py

Line 28 in 403b242

from xlsxwriter.utility import datetime_to_excel_datetime, xl_rowcol_to_cell

This is because in release 3.2.1 they changed it to a private function i.e. _datetime_to_excel_datetime
https://github.com/jmcnamara/XlsxWriter/blob/6abc6b49a8fe25954fb8e61f74ea16a76c467b6b/xlsxwriter/utility.py#L908-L959

[ollyhensby]

Resolved here: #12