.adoc extension insted of title

[Alessio Ciregia]

Hello.
I would like to report that, at least in the installation guide for F28,
the menu presents something like filename.adoc instead of the title of the
chapter.
For instance Preparing_for_Installation.adoc and subchapters

<https://docs.fedoraproject.org/en-US/fedora/f28/install-guide/>

Thanks.
Ciao,
A.