Reference to an other sheet in formula

Hi, I have a problem using formula and Sheet reference.

I am using this :
```

sheet.getCell('A2').dataValidation = {
type: 'list',
allowBlank: true,
formulae: ['Company.A2:A500'],
showInputMessage: true,
promptTitle: 'Company',
prompt: 'In which company the user is in.',
};
```

And when I generate the XLSX and open the file with _libre office_ I get **'company.a2:A500'** in data validation and it don't work.

I guess there is a bug in Sheet name handling, at some point you seems to put some data in lowercase.

If you have a patch I take it please! :)

**PS**: I did try this too, and it gives the same behavior

```
sheet.getCell('A2').value = {
formula: 'Company.A10',
value: '',
};
```