calculate RegExp once instead of on every check

[chrisblossom]

This is an optimization for creating the regex checks for each type of card. Previously the check was created every time the number was checked. Now it is created once when the module is loaded.

[crookedneighbor]

Hey @chrisblossom, thanks for submitting this. It's definitely a more performant solution, but as it turns out, we're working on some other optimization strategies that will conflict with this change, so I'm going to close this now.

Thanks again for your interest in this project!