The bugfix 71722fa in #19 meant to make the http-layer install properly on python3 and python2 has not been propagated to PyPI, such that pip3 install scapy-http still results in the same error which as been noted as fixed.
pip3 install git+https://github.com/invernizzi/scapy-http@df0caa6f38a88e45f64dff0bb3cdfaceee270ae2
The above command meanwhile has the intended results.