Log Message:
py-xlsxwriter: updated to 1.2.7

Release 1.2.7:

* Fix for duplicate images being copied to an XlsxWriter file. Excel uses an
  optimization where it only stores one copy of a repeated/duplicate image in
  a workbook. XlsxWriter didn't do this which meant that the file size would
  increase when then was a large number of repeated images. This release fixes
  that issue and replicates Excel's behavior.

* Added documentation on :ref:`num_format_categories` and
  :ref:`num_format_locale`.

* Added note to :func:`protect()` about how it is possible to encrypt an
  XlsxWriter file using a third party, cross platform, open source tool called
  `msoffice-crypt <https://github.com/herumi/msoffice>`_.