How to install Rasa on Mac OS?

I keep getting this error when I try to install Rasa on Mac. Does anyone know how to solve?

Hi @ParthN, which version of python are you using?

Hi @erohmensing, thank you for replying I am using 3.6.7

Hm are you sure about that? Seems like encoding is a supported keyword for all of python 3: Backporting Python 3 open(encoding="utf-8") to Python 2 - Stack Overflow

Could you maybe try

pip3 install rasa-x --extra-index-url