No module named openhtf.output.web_gui.__main__;

I'm following:
https://github.com/google/openhtf/blob/master/CONTRIBUTING.md

When I execute the following command:
`python -m openhtf.output.web_gui`

I get the error:
`... Python\Python37-32\python.exe: No module named openhtf.output.web_gui.__main__; 'openhtf.output.web_gui' is a package and cannot be directly executed
`
I tried executing the command in different subfolders of openhtf, without success.
I followed the previous steps with success.

I'm working on a Windows 7.