Update invoice_fiscal_position_update with better use of the new API
Inspired by the work of @eLBati on purchase_fiscal_position_update
Use double quotes around docstring to please my friend Pedro :)
Add self.ensure_one()
Merge pull request #26 from akretion/8.0-fp-update-better-new-api

Update invoice_fiscal_position_update with better use of the new API