You can generate the e-book files manually with Asciidoctor.
If you run the following you may actually get HTML, Epub, Mobi and PDF output files:
$ bundle install
$ bundle exec rake book:build
Converting to HTML...
-- HTML output at progit.html
Converting to EPub...
-- Epub output at progit.epub
Converting to Mobi (kf8)...
-- Mobi output at progit.mobi
Converting to PDF...
-- PDF output at progit.pdf
You can generate just one of the supported formats (HTML, EPUB, mobi, or PDF).
Use one of the following commands:
To generate the HTML book:
$ bundle exec rake book:build_html
To generate the EPUB book:
$ bundle exec rake book:build_epub
To generate the mobi book:
$ bundle exec rake book:build_mobi
To generate the PDF book:
$ bundle exec rake book:build_pdf