Make heavy dependencies as peer dependencies

[vittoriozamboni]

Hi!

Thank you for the amazing docz work, I find it great to use and build documentations.
I am currently using this plugin in many sites, but unfortunately in few projects node-sass is not an option to be installed due to the way it is compiled.

Would it be possible to put it, with less and postcss, as peer dependencies?
It seems to be an overload to install all these dependencies in order to use simple CSS.