Update .gitlab-ci.yml

2 jobs for master in 0 seconds
Status Job ID Name Coverage
  Build
failed #32869
build-doc

00:00:00

failed #32846
build-doc

00:00:00

 
Name Stage Failure
failed
build-doc Build
Fetching changes with git depth set to 50...
Reinitialized existing Git repository in /home/gitlab-runner/builds/gxiMTsvf/0/2017bentrioum/markovprocesses.jl/.git/
Checking out 0b4ea1e3 as master...
Skipping Git submodules setup
Executing "step_script" stage of the job script
$ julia --project=docs/ -e 'using Pkg; Pkg.develop(PackageSpec(path=pwd())); Pkg.instantiate()'
bash: line 98: julia: command not found
Cleaning up file based variables
ERROR: Job failed: exit status 1