get_contacts tax_number_type, invalid value "TAXNUMBERTYPE/SSN"

I'm getting an error just querying the contacts of a tenant.
```
ValueError: Invalid value for `tax_number_type` (TAXNUMBERTYPE/SSN), must be one of ['SSN', 'EIN', 'ITIN', 'ATIN', 'None']
```

Using xero-python 9.2, will downgrade to 9.1 which I think should fix it since tax_number_type was just added to contacts API.