ModuleNotFoundError: No module named 'rdfa'

I installed the module as you said
 ```
 pip install git+git://github.com/tetherless-world/markdown-rdfa.git#egg=markdown-rdfa
 ```
Then when trying to use it:
```
python -m markdown -x rdfa example.rmd
```
The error `ModuleNotFoundError: No module named 'rdfa'` is displayed.
Does anyone know whats going on?