etherpad.js does not get minified correctly with minify@5.2.0. Instead 
of the minified js, there is just 'Promise { <pending> }'. minify@5.1.1 
works correctly

Minify v6 requires node>=12

https://team.picasoft.net/picasoft/pl/gd5e6y48p3gfupp9tgnchqgw6e

This will fix permissions issues : a Docker Volume mounted on a non-existing directory will be owned by root, but we run Etherpad as etherpad. As such we have no way of writing in the mounted directory