Update zurb version in factory-setup.adoc

Same issue as reported by @youribonnaffe here: https://github.com/asciidoctor/asciidoctor-stylesheet-factory/pull/8

So all credits for this one goes to @youribonnaffe thank you mate you really made my Monday easier, and I had the same issue 'Otherwise compilation fails with error: Line 5 of _global.scss: Undefined mixin 'box-sizing'. - I had this issue because I did not use bundle to install the dependencies (I used gem install)'

Ciao ciao