Make "Publish" work with mainnet txs

[caffeinum]

Currently, it's hardcoded that it uses web3 to rinkeby. That should not matter for decoding, but publish will fail, if on the wrong network.

[ohld]

I think, I've found the line that may help.
https://github.com/flightwallet/decode-eth-tx/blob/master/index.html#L72