VectorSerializer methods don't match signature of base

[ghtdak]

additional parameter inner_cls

https://github.com/petertodd/python-bitcoinlib/blob/master/bitcoin/core/serialize.py#L237

[petertodd]

Good catch! I added a FIXME comment to the code in question noting that the API design isn't optimal. Just removing that parameter isn't ok though, as it is needed.