Update .gitlab-ci.yml

1 job for master in 17 seconds (queued for 3 seconds)
Name Stage Failure
failed
build Test
From https://transfer.hft-stuttgart.de/gitlab/hft_gitlab/regionchooser
* [new ref] refs/pipelines/271 -> refs/pipelines/271
5c1fe9a..cc19912 master -> origin/master
Checking out cc199121 as master...

Skipping Git submodules setup
$ mvn package -B
/bin/sh: eval: line 81: mvn: not found
ERROR: Job failed: exit code 127