Use nanoc-live instead of guard-nanoc

nanoc-live has now reached a stable version 1.0.0 and can be used to replace guard-nanoc.

Advantages over guard-nanoc:

• It provides a clear output of the files that are being updated during the (re)build.
• It reloads the page automatically until the site is built.
• This might fix the macOS bug.

Nothing changes in how you run Nanoc to preview the changes. The commands are the same.