Please generate devhelp index format v2

Problem

Sphinx in devhelp mode generates index file format v1, which is deprecated

Procedure to reproduce the problem

• Have GNOME 3.28
• Build and install https://github.com/Mic92/python-mpd2
• Run devhelp

Error logs / results

Apr 23 11:20:24 espresso devhelp[32481]: The file 'file:///usr/share/devhelp/books/python-mpd2/python-mpd2.devhelp.gz' uses the Devhelp index file format version 1, which is deprecated. A future version of Devhelp may remove the support for the format version 1. The index file should be ported to the Devhelp index file format version 2.

Environment info

• OS: Debian GNU/Linux unstable (development branch) with GNOME 3.28
• Python version: python3.6 3.6.5-3 from Debian
• Sphinx version: 1.7.2-4 from Debian
• devhelp 3.28.1-1 from Debian