Digifinex: fetchOrder, add swap support
Digifinex: fetchOrder, add swap support

Swap requires order to be entered like this '"1590923061186531328"' since the id's are only numbers.

### fetchOrder:
```
digifinex.fetchOrder (1590923061186531328, ETH/USDT:USDT)

{
  info: {
    order_id: '1590923061186531328',
    instrument_id: 'ETHUSDTPERP',
    margin_mode: 'crossed',
    contract_val: '0.01',
    type: '1',
    order_type: '0',
    price: '900',
    size: '6',
    filled_qty: '0',
    price_avg: '0',
    fee: '0',
    state: '0',
    leverage: '20',
    turnover: '0',
    has_stop: '0',
    insert_time: '1668140590372',
    time_stamp: '1668140590372'
  },
  id: '1590923061186531328',
  clientOrderId: undefined,
  timestamp: 1668140590372,
  datetime: '2022-11-11T04:23:10.372Z',
  lastTradeTimestamp: 1668140590372,
  symbol: 'ETH/USDT:USDT',
  type: 'limit',
  timeInForce: undefined,
  postOnly: undefined,
  side: 'open long',
  price: 900,
  stopPrice: undefined,
  amount: 6,
  filled: 0,
  remaining: 6,
  cost: 0,
  average: undefined,
  status: 'open',
  fee: { cost: 0 },
  trades: [],
  fees: [ { cost: 0 } ]
}
```

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