AttributeError: module 'plugins.pelican-toc' has no attribute 'register'

I was trying to replicate the book Make build in EPUB or PDF and seems to be failing because of Pelican external sources.

I'd be a great idea to include instructions on how to replicate the build easily. I'd be nice to collaborate without the hassle of setting up with this kind of errors. 

Any suggestions would be highly appreciated. 