Travis: change how 'python-systemd' is installed
Travis: change how 'python-systemd' is installed

Get Travis to install it using APT instead of pip to ensure that
all of the dependencies are taken care of properly

guyfawcus/ArchMap,guyfawcus/ArchMap,maelstrom59/ArchMap,guyfawcus/ArchMap,maelstrom59/ArchMap