Merge branch 'bc/doc-use-docbook-5'

Start using DocBook 5 (instead of DocBook 4.5) as Asciidoctor 2.0 no longer works with the older one. * bc/doc-use-docbook-5: Documentation: fix build with Asciidoctor 2

Junio C Hamano committed Oct 6, 2019 at 12:25 UTC faf5576a8d749c7c46fafd0c62da47ec078e1486

No changes.