shouldn it be 'iban' ...
shouldn it be 'iban' ...

... as the class is callen `IbanValidator` and not `IbanFieldValidator`... 
using `validates :iban_string, iban_field: true` causes `Unknown validator: 'IbanFieldValidator'`
kaspernj/validates_iban,kaspernj/validates_iban,kaspernj/validates_iban