ZD6408885: Correction to card number

ZD6408885 Correction to a card number that needs to be 15 digits instead of 16 digits

Author: manishlad-cs

source/testing_govuk_pay/index.html.md.erb

@@ -129,7 +129,7 @@ There are separate sets of mock card numbers for:
 |Successful payment |4131840000000003| Visa | Debit - corporate prepaid |
 |Successful payment |4111111111111111| Visa | Credit - corporate |
 |Successful payment |4000000000000010| Visa | Credit or debit |
-|Successful payment |2221000000000000| Mastercard | Credit |
+|Successful payment |222100000000000| Mastercard | Credit |
 |Successful payment |5105105105105100| Mastercard | Debit |
 |Successful payment |5200828282828210| Mastercard | Debit |
 |Successful payment |371449635398431| American Express | Credit |