Argentina formatting update

Thanks for the patch.

The sources I have found tell me that it is correct as it is. Do people sometimes not use the final three letters? Perhaps they should be optional.

There is no point putting {1}; it means the same thing as leaving it out. While we are changing it, it should use \d instead of [0-9].

Everything I have read about Argentine postal codes matches what is currently there. If it is the case that people are not actually using the last three digits, those can be made optional.

Did you want to re-roll this with the last three digits optional?

As far as I can tell, the code is correct as it in. I would be interested in hear from someone with experience with Argentinian postal codes. I'm happy to make fixes as required.