Update byobu to v6
While investigating why https://bugs.launchpad.net/ubuntu/+source/byobu/+bug/2064030 is not affecting Arch, I saw that Arch is still on v5 of byobu. The v6 releases seem to only be published on Github. I made an Issue for wrong links to that here.
As this update does break login over ssh with byobu autostart and fish, we might want to wait until https://bugs.launchpad.net/ubuntu/+source/byobu/+bug/2064030 is fixed.