Fixing a date issue about one millisecond before midnight

[krisanselmo]

Description

This PR fix a formatting date issue when typically we manipulate a date that is 1 millisecond before midnight.
The internal usage of .toFixed(7) round the date value to the next day.

Step to reproduce:

const workbook = new Workbook();
const worksheet = workbook.addWorksheet();
worksheet.cell(1, 1).date(new Date('2017-06-01T23:59:59.999Z'));

Result

[jrohland]

Thanks for the PR and updated test. I will review and get a new version up soon with the dependency updates that are pending as well.