Ascendex fetchBalance
Ascendex fetchBalance

Adjusted margin functionality for fetchBalance:
```
ascendex.fetchBalance ()
2022-06-22T01:52:00.673Z iteration 0 passed in 1791 ms

{
  info: {
    code: '0',
    data: [
      {
        asset: 'USDT',
        totalBalance: '48.949901399',
        availableBalance: '48.949901399',
        borrowed: '0',
        interest: '0'
      }
    ]
  },
  timestamp: 1655862720672,
  datetime: '2022-06-22T01:52:00.672Z',
  USDT: { free: 48.949901399, used: 0, total: 48.949901399 },
  free: { USDT: 48.949901399 },
  used: { USDT: 0 },
  total: { USDT: 48.949901399 }
}
```

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