Log Message:
py-openpyxl: updated to 2.6.1

2.6.1:
Bugfixes
* ReadOnlyCell.is_date does not work properly
* Cannot read Google Docs spreadsheet with a Pivot Table
* Charts created with openpyxl cannot be styled
* Cannot handle some numpy number types
* Exception when reading unknowable number formats
* Only last formatting rule for a range loaded
* Give MergedCell a value attribute
* Cannot process worksheets with comments
* Cannot process worksheets with both row and page breaks
* Cannot reset dimensions in ReadOnlyWorksheets
* Incorrect descriptor in ParagraphProperties
* Missing hier attribute in PageField raises an exception