Change docbooks in order to make Krusader build at least under (K)Ubuntu 18.04…

Authored by asensi on Jan 22 2020, 9:31 PM.

Description

Change docbooks in order to make Krusader build at least under (K)Ubuntu 18.04 LTS and in docs.kde.org

Differential Revision: https://phabricator.kde.org/D26817