Allow filtering logs by settlements

[kyungmin]

https://api.balancedpayments.com/logs?endpoint=settlements&... returns the following error:

{
  "errors": [
    {
      "status": "Bad Request",
      "status_code": 400,
      "description": "Field \"endpoint\" value \"settlements\" is not not one of \"credits\",\"debits\",\"holds\",\"refunds\",\"accounts\",\"cards\",\"bank_accounts\",\"customers\",\"reversals\" Your request id is OHM5d07cd4ca80211e48c5306429171ffad.",
      "request_id": "OHM5d07cd4ca80211e48c5306429171ffad"
    }
  ]
}