Update .gitlab-ci.yml

1 job for master in 4 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
failed build #4804

00:00:04

 
Name Stage Failure
failed
build Build
Reinitialized existing Git repository in /builds/peter.eder/pandoc/.git/
Checking out c65ca5ab as master...

Skipping Git submodules setup
Executing "step_script" stage of the job script
$ ssh-keyscan -Ht rsa [gitlab.ce.jku.at],[140.78.73.44] >> ~/.ssh/known_hosts
/bin/bash: line 98: /root/.ssh/known_hosts: No such file or directory
Cleaning up file based variables
ERROR: Job failed: exit code 1