CBU functions should throw an exception when the number is not valid.

[hnicodemo]

I think getAssociatedBank, getBankCode y getBranch should start with:

if (!isValid(cbu)) throw new Error('CBU is not valid);

[miparnisari]

@hnicodemo please create a PR and i'll have a look. Thanks!

[gastonelhordoy]

As a validation library I would suggest not to throw errors. IMHO doing so is a highly opinionated assumption.

Developers using this lib should decide what to do upon an invalid value, either throwing an error, providing a more detailed explanation of the issue in the context of the app or whatever makes sense to them.

Excellent work BTW, I would probably contribute adding new banks like Wilobank.