can't install powerbi-visuals-tools

Greetings,

I am interested in starting to get my hands on creating custom visuals and as I am following a guideline to do prerequisite installations that is offered here. 

Basically, I need to install powerbi-visuals-tools from cmd. I already downloaded Nodejs and npm. The error I get is the following after running it:

Is there something I'm missing or not correctly configured to get this up and running?

Thanks in advanced!