raise 'The `nanoc-asciidoctor` gem is obsolete as of Nanoc 4.8.0. To upgrade:

1. In your Gemfile, make sure that Nanoc is at least version 4.8, e.g.
       gem \'nanoc\', \'~> 4.8\'

2. Remove `gem \'nanoc-asciidoctor\'` from your Gemfile

3. Remove `require \'nanoc-asciidoctor\'` from anywhere in your site

4. Run `bundle install`'