fix(period): wrong name for validator address attribute in period options

[troggy]

getPeriodByBlockHeight API returns validatorAddress, not ownerAddress:

curl --location --request POST 'https://testnet-node.leapdao.org/' \
--header 'Content-Type: application/json' \
--data-raw '{
  "method": "plasma_getPeriodByBlockHeight",
  "params": ["190000"],
  "id": 1,
  "jsonrpc": "2.0"
}'

returns

{
    "jsonrpc": "2.0",
    "id": 1,
    "result": [
        {
            "periodStart": 189984,
            "periodEnd": 190015,
            "casBitmap": "0xc000000000000000000000000000000000000000000000000000000000000000",
            "slotId": "0",
            "validatorAddress": "0xDe42468b9ba193384eA76e337BAe1676932133Cf"
        }
    ]
}