ci: Update gitlab-ci.yml

2 jobs for master in 27 seconds (queued for 2 seconds)
Name Stage Failure
failed
test-pylint Test

$ coverage run --source=nbxmpp -m unittest discover -v
/bin/bash: line 122: coverage: command not found
Uploading artifacts for failed job
Uploading artifacts...
WARNING: coverage.xml: no matching files
ERROR: No files to upload
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1