docker demo fails to build image due to errors(?) in Dockerfile

[floridop]

Motivation

I tried the docker demo on Ubuntu 18.04 and it fails during the build process due to errors in the docker file, namely this line:
https://github.com/rucio/rucio/blob/master/etc/docker/demo/Dockerfile#L16
I think neither sudo nor the plus sign should be in that line.
It worked after removing those

Modification

remove of sudo and the + sign from
https://github.com/rucio/rucio/blob/master/etc/docker/demo/Dockerfile#L16