fix(isVAT): fixed KZ VAT number length check

[MatthieuLemoine]

According to Wikipedia and the source linked in this article, Kazakh VAT numbers are 12 digits long, not 9.

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (b958bd7) 99.95% compared to head (6fa00af) 99.95%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2279   +/-   ##
=======================================
  Coverage   99.95%   99.95%           
=======================================
  Files         107      107           
  Lines        2454     2454           
  Branches      619      619           
=======================================
  Hits         2453     2453           
  Partials        1        1           

Files Changed	Coverage Δ
src/lib/isVAT.js	100.00% <100.00%> (ø)

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