I'm trying to hash a message as shown here:

```
function constructPaymentMessage(contractAddress, amount) {
  return ethereumjs.ABI.soliditySHA3(
    ["address", "uint256"],
    [contractAddress, amount],
  );
}

```

how can I use `web3.sha3` instead of `ABI.soliditySHA3` to get the SHA3 hash correctly, is there any difference anyway? thanks.