Update build setup

[thypirate]

Hello there, i updated from gulp 3.6.0 to gulp 4.0 and also made necessary changes to gulpfile because i had node version 14.18.1 (didn´t want to use nvm) and couldn't get the project to build because compatibility issues but now im able to generate pdf (i haven´t tried to generate epub and generate site doesn´t work ) but since it is a some what old project i was wondering if i can make some changes to update the build setup in order to work with latest version of gulp and node.

Btw amazing book.