eth.contract method result not iteratable

should be able to write
```js
  const [ resultBn ] = await uniswapv1Dai.getEthToTokenInputPrice(oneEth)
```

error
```
TypeError: (intermediate value) is not iterable
```

workaround
```js
  const { 0: resultBn } = await uniswapv1Dai.getEthToTokenInputPrice(oneEth)
```