Use the ActiveMerchent company specific credit card regexes

@ggrossman 

This makes it so we use Shipify's beautiful activemerchent gem.

Should I add tests for the `brand?` method?
They are all here  https://github.com/Shopify/active_merchant/blob/master/test/unit/credit_card_methods_test.rb
how about:
```Ruby
CARD_COMPANY_PREFIXES = {
  12 => %r(\A(?:
    (?:5[06-8]|6)                 | # maestro
    (?:6304|6706|6709|6771(?!89)) | # laser
))x, ...
}
```