Refactor preview parsing

[gilbarbara]

It should work with Amex, Diners, 16, and 19 characters.

[cassiocardoso]

I was checking this issue and I noticed this line:

https://github.com/amarofashion/react-credit-cards/blob/master/src/index.js#L74

Given the logic below where the try to update the maxLength depending on the number passed, I don't think it's necessary to set the maxLength to 19 if it is in preview mode.

I did some tests locally with 16, 19 digit cards as well the Diners type mentioned in issue #70 and it appears to solve our issues.

@gilbarbara what do you think? Any edge cases that you can think of?

[gilbarbara]

Actually the task is to handle formatting with these cards and not exactly detect the maxLength.
MaxLenght is just a safeguard to avoid breaking the UI.

Is that it?

[cassiocardoso]

This is what I noticed locally while testing with the number provided in issue #70 (preview mode - Diners card w/ 14 digits):

(notice the extra bullet at the end of the number)

That's why I thought we would need to update maxLength for this case.