asciidoctor: ERROR: progit.asc: line 53: only book doctypes can contain level 0 sections

[rpjday]

The recent change to progit.asc now generates:

$ bundle exec rake book:build
Generating contributors list
Converting to HTML...
asciidoctor: ERROR: progit.asc: line 53: only book doctypes can contain level 0 sections
-- HTML output at progit.html

rday

[jnavila]

Bisected to f2678ab

Quite strange as this patch doesn't change the structure of the book.

[rpjday]

I am as baffled as you, for just that reason. Is no one else seeing this? Perhaps I have an updated version of asciidoctor that introduced this.

P.S. My generated PDF does not contain the colourful cover page, just the text "Pro Git", then the authors' names. So something is definitely borked.