for vat numbers from FI, allow 0 as last digit

[jbrinksmeier]

This is a mitigation for #95
For FI VAT numbers, implementation of this algorithm

VAT format: [C1 C2 C3 C4 C5 C6 C7 C8]

Range:
C2 .. C8 Numeric from 0 to 9

Rules:
C8
R = 11 - (7C1 + 9C2 + 10C3 + 5C4 + 8C5 + 4C6 + 2*C7) modulo11
If R = 10 then, VAT number is invalid
If R = 11 then C8 = 0
Else C8 = R

lacks acceptance for

if R = 11 then C8 = 0

This PR adds that case as valid VAT

[krzaczek]

Looks good ..

[DragonBe]

Looks good to me, let me merge it in.