Fix the getBalance function and its uses in examples

[chmanie]

The getBalance method is too confusing.

If it's called without the second argument e.g. for Colony 0x8e389bf45f926dDDB2BE3636290de42B68aefd51, it will throw an error:

Found an error: missing revert data in call exception; Transaction reverted without a reason string [ See: https://links.ethers.org/v5-errors-CALL_EXCEPTION ] (data="0x", transaction={"to":"0xCCcccdCC0CcF6C708D860e19353c5f9a49ACccCc","data":"0x70a082310000000000000000000000008e389bf45f926dddb2be3636290de42b68aefd51","accessList":null}, error={"reason":"processing response error","code":"SERVER_ERROR","body":"{"jsonrpc":"2.0","id":64,"error":{"code":-32000,"message":"execution reverted"}}\n","error":{"code":-32000},"requestBody":"{"method":"eth_call","params":[{"to":"0xcccccdcc0ccf6c708d860e19353c5f9a49accccc","data":"0x70a082310000000000000000000000008e389bf45f926dddb2be3636290de42b68aefd51"},"latest"],"id":64,"jsonrpc":"2.0"}","requestMethod":"POST","url":"[https://app.colony.io/public-rpc/"%7D](https://app.colony.io/public-rpc/%22%7D), code=CALL_EXCEPTION, version=providers/5.7.2)

Adjust its uses in examples