Perhaps a really dumb question, but you made sure to confirm you have the executable at /usr/bin/julia? Ie,
$ ls /usr/bin
shows that julia is there (and not, for example, in /usr/local/bin)? You can also try that running $ /usr/bin/julia from the command line launches Julia.
Thanks for your work on the julia plug-in in VS Code. I installed VS Code with julia plug-in on all my machines (2 windows, 1 fedora, 1 centos) today, and I think I finally find the right editor for Julia.
Personal opinion:
Atom it is just too slow, and takes too much cpu capacity when it is running. Also, I did not notice that it is almost 1G in windows and about 450 MB in Linux until I uninstalled it today, that is larger than most languages themselves.