Use system Julia instead of installing it
Use system Julia instead of installing it

* [CI] Use system Julia instead of installing it

Since [release 20200308](https://github.com/actions/virtual-environments/releases/tag/ubuntu18%2F20200308.0) of the GH Actions environments, the latest version of Julia is preinstalled on the GH Actions VMs.

* Update concepts.csv

(to trigger a build)

exercism/xjulia