Change description of Greek FPA number
Change description of Greek FPA number

In Greece, our VAT number is used as a generic "tax registration" num.
Update the docstring to reflect that name.

arthurdejong/python-stdnum,t0mk/python-stdnum,arthurdejong/python-stdnum,arthurdejong/python-stdnum,holvi/python-stdnum,holvi/python-stdnum,dchoruzy/python-stdnum,holvi/python-stdnum