Bittrex fetchOpenOrders 'stop'
Bittrex fetchOpenOrders 'stop'

Added stop order functionality to fetchOpenOrders:
```
node examples/js/cli bittrex fetchOpenOrders BTC/USDT undefined undefined '{"stop":"true"}'

bittrex.fetchOpenOrders (BTC/USDT, , , [object Object])
2022-04-20T02:43:48.074Z iteration 0 passed in 1711 ms

                                  id | clientOrderId |     timestamp |                 datetime | lastTradeTimestamp |   symbol |  type | timeInForce | postOnly | side | price |  stopPrice | cost | average | amount | filled | remaining | status |                 fee | trades |
         fees
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
f64f7c4f-295c-408b-9cbc-601981abf100 |               | 1650422292260 | 2022-04-20T02:38:12.260Z |      1650422292260 | BTC/USDT | limit |
   GTC |    false |  buy | 30000 | 0.10000000 |      |         | 0.0002 |        |           |   open | {"currency":"USDT"} |     [] | [{"currency":"USDT"}]
1 objects
```

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