API Legacy Invoice Credits Error Message Format Change

The following changes were made in the format of errors messages returned from the Invoices: Credits endpoint. This change was made for consistency in order to mirror other API endpoints.

New Format

{
    "errors": [
        "Amount: is not a number."
    ]
}
<?xml version="1.0" encoding="UTF-8"?>
<strings type="array">
    <string>Amount: is not a number.</string>
</strings>

Old format

{
    "errors": {
        "amount_in_cents": [
            "Amount: is not a number."
        ]
    }
}
<?xml version="1.0" encoding="UTF-8"?>
<errors>
    <error>Amount: is not a number.</error>
</errors>