Incorrect Content-Type header for exported XLSX

[tchamberlin]

Content-Type header for exported .xlsx files is incorrectly set to application/vnd.ms-excel. This causes e.g. Firefox to incorrectly indicate the file type of the download as "Microsoft Excel 97-2003 Worksheet". It also results in the following error when opening directly in Excel (at least for Windows 10/Firefox/Excel 2019): "The file format and extension of 'table.xlsx-1.xls' don't match. The file could be corrupted or unsafe. ...". The files do open after that, but the error is a bit unsettling.

The MIME type of the resultant file is correct:

$ file --mime-type -b table.xlsx
application/vnd.openxmlformats-officedocument.spreadsheetml.sheet

The fix here is to change this line to indicate the correct content type of application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.

I've tested the above change, and it behaves as expected. I'm happy to open a PR if that is helpful

Thanks!

[jieter]

Thanks for the report, a pull request is very welcome.