Added symbol and rate required params to isolated borrowMargin
Added symbol and rate required params to isolated borrowMargin

Isolated borrowMargin:
```
node examples/js/cli gate borrowMargin USDT 100 LTC/USDT '{"rate":"0.0002"}'

gate.borrowMargin (USDT, 100, LTC/USDT, [object Object])
2022-06-28T05:31:18.982Z iteration 0 passed in 310 ms

{
  id: 34267439,
  currency: 'USDT',
  amount: 100,
  symbol: 'LTC/USDT',
  timestamp: 1656394279,
  datetime: '1970-01-20T04:06:34.279Z',
  info: {
    id: '34267439',
    create_time: '1656394279',
    expire_time: '1657258279',
    status: 'loaned',
    side: 'borrow',
    currency: 'USDT',
    rate: '0.0002',
    amount: '100',
    days: '10',
    auto_renew: false,
    currency_pair: 'LTC_USDT',
    left: '0',
    repaid: '0',
    paid_interest: '0',
    unpaid_interest: '0.003333333333'
  }
}
2022-06-28T05:31:18.982Z iteration 1 passed in 310 ms
```

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