Simplify repayMargin by using different endpoints
Simplify repayMargin by using different endpoints

```
node examples/js/cli kucoin repayMargin USDT 100.00008333 BTC/USDT '{"marginMode":"isolated"}'

kucoin.repayMargin (USDT, 100.00008333, BTC/USDT, [object Object])
2022-07-26T02:34:41.072Z iteration 0 passed in 513 ms

{
  id: undefined,
  currency: 'USDT',
  amount: 100.00008333,
  symbol: 'BTC/USDT',
  timestamp: 1658802881072,
  datetime: '2022-07-26T02:34:41.072Z',
  info: { code: '200000', data: null }
}
2022-07-26T02:34:41.072Z iteration 1 passed in 513 ms
```

```
node examples/js/cli kucoin repayMargin USDT 100.00008333

kucoin.repayMargin (USDT, 100.00008333)
2022-07-26T02:36:33.125Z iteration 0 passed in 502 ms

{
  id: undefined,
  currency: 'USDT',
  amount: 100.00008333,
  symbol: undefined,
  timestamp: 1658802993125,
  datetime: '2022-07-26T02:36:33.125Z',
  info: { code: '200000', data: null }
}
2022-07-26T02:36:33.125Z iteration 1 passed in 502 ms
```

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