Update .gitlab-ci.yml

1 job for master in 5 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
failed build #4772

00:00:05

 
Name Stage Failure
failed
build Build
fatal: could not read Username for 'https://gitlab.ce.jku.at': No such device or address
fatal: clone of 'https://gitlab.ce.jku.at/simon.wimmer/pandoc_pdf_tool.git' into submodule path '/builds/peter.eder/pandoc/pandoc_pdf_tool' failed
Failed to clone 'pandoc_pdf_tool'. Retry scheduled
Cloning into '/builds/peter.eder/pandoc/pandoc_pdf_tool'...
fatal: could not read Username for 'https://gitlab.ce.jku.at': No such device or address
fatal: clone of 'https://gitlab.ce.jku.at/simon.wimmer/pandoc_pdf_tool.git' into submodule path '/builds/peter.eder/pandoc/pandoc_pdf_tool' failed
Failed to clone 'pandoc_pdf_tool' a second time, aborting
Cleaning up file based variables
ERROR: Job failed: exit code 1