http-prompt: fix build

I don't really understand why this works:

- Building with python3 because python2 fails with "error: invalid command
'bdist_wheel'".
- Specifying the path to prompt_toolkit v1 because otherwise the dependency
resolution fails with "ERROR: Could not find a version that satisfies the
requirement prompt-toolkit<2.0.0,>=1.0.0 (from http-prompt==1.0.0) (from
versions: none) ERROR: No matching distribution found for
prompt-toolkit<2.0.0,>=1.0.0 (from http-prompt==1.0.0)".