Example of a customerDriversLicense that gets through validation.

This is validation at the gateway rather than locally. The documentation
is lacking on this field and its values, but it does seem to be US-only
driving licence details.

README.md

@@ -74,7 +74,11 @@ $response = $gateway->authorize([
     // Additional optional attributes:
     'customerId' => '123456',
     'customerType' => \Academe\AuthorizeNet\Request\Model\Customer::CUSTOMER_TYPE_INDIVIDUAL,
-    ~~'customerDriversLicense' => [TBC],~~
+    'customerDriversLicense' => [
+        'number' => '123456',
+        'state' => 'NY',
+        'dateOfBirth' => '1967-01-01',
+    ],
     'customerTaxId' => 'TAX456',
 ])->send();