ids are not int but string
ids are not int but string

Follows #261, #263 and #270  on phpdoc types.

According to [the official documentation](https://docs.mangopay.com/endpoints/v2.01/transactions#e222_the-transaction-object), `DebitedWalletId`, `CreditedWalletId`, `AuthorId` and `CreditedAuthorId` are string, not int.
Mangopay/mangopay2-php-sdk,Mangopay/mangopay2-php-sdk