Extend number length for visa electron (#29)

* Extend number length for visa electron

Visa Electron card also can be 17 digits long, please test with these card details:

Card Number: 49174917491749174

CV2/CVV: 123

* added 17 digits long credit card number to tests

Author: stefanheimann

src/Cards/VisaElectron.php

@@ -39,7 +39,7 @@ class VisaElectron extends Card implements CreditCard
      *
      * @var array
      */
-    protected $number_length = [16];
+    protected $number_length = [16, 17];
 
     /**
      * CVC code length's.

tests/Unit/Cards/VisaElectronTest.php

@@ -18,6 +18,7 @@ public function validNumbers(): Collection
             '4917300800000000',
             '4479651508787615',
             '4113550663468031',
+            '49174917491749174',
         ]);
     }