xslx export broken with TypeError: cell() takes at least 3 arguments (2 given)

To fix this issue you need to add this version-pinn: `openpyxl = 2.4.9` untill a new version of tablib is released (currently it is at version 0.11.5).

Here is the traceback:

```python-traceback
Traceback (innermost last):
Module ZPublisher.Publish, line 138, in publish
Module ZPublisher.mapply, line 77, in mapply
Module Products.PDBDebugMode.runcall, line 70, in pdb_runcall
Module ZPublisher.Publish, line 48, in call_object
Module collective.contentexport.browser.export, line 192, in __call__
Module tablib.formats._xlsx, line 43, in export_set
Module tablib.formats._xlsx, line 122, in dset_sheet
TypeError: cell() takes at least 3 arguments (2 given)
```