Corrections to get "nonante" for 90 in French from Belgium

[jejust]

In spite of what is said in the documentation, "quatre-vingt-dix" was used even with the belgian option
(everything else was correct).

With this patch, the output is really "nonante" for 90, and the rest is consistent with this table:

Option	70	80	90
france	soixante-dix	quatre-vingts	quatre-vingt-dix
belgian	septante	quatre-vingts	nonante
swiss	septante	huitante	nonante

Thank you, @nlct and @vincentb1, for this package!