Support for other EVM based Etherscan chains

[miohtama]

The README mentions Ropsten, Kovan, etc.

But is the library compatible with other L1 or L2 based chains that run their own hosted EtherScan instances, like polygonscan.com?

[github-actions]

Thanks for reporting this issue, we are on it :)

[gnarvaja]

I submitted this #27 that adds support for Polygon and allows to easily support other instances when the domain is not etherscan.io.