Playground built from latest GitHub does not show any visuals

I cloned the PowerBI-visuals source from GitHub and built it by following the proceedure found in https://github.com/Microsoft/PowerBI-visuals . I used gulp to run the build instead of VS2015 as I have read about  issues reported with VS2015.

Once the build is completed I can launch the Playground web app but none of the visuals are available. I only get empty dropdowns for visuals and data sets.

In short here are the commands I ran after installing GitHub and Node.js (v4.4.5 LTS) and getting a copy of the source (commands running from the GitHub\PowerBI-visuals folder):

npm install -g gulp
npm install          # This command installed depencies for PowerBI-visuals
gulp build
gulp run:_playground    # Actual command does not have an _ 

Thanks for your help.