Erroneous "counterparty" field included for XRP in GET balance_changes response

[professorhantzen]

The "counterparty" field containing a duplicate of the "amount_change" field, on balance changes of XRP (which should never have a "counterparty" field), appears several times on this request:

https://data.ripple.com/v2/accounts/rDG9CNs9ReqEkiB8JN5QgYBdkUvxpoG4CU/balance_changes/?start=2016-01-11T12:37:00Z