Use headless chromium for karma

1 job for <span class="ref-name">gitlab-ci-test</span> in 8 minutes and 47 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #2900
test

00:08:47

 
Name Stage Failure
failed
test Test
14 06 2018 14:13:04.729:INFO [launcher]: Trying to start ChromiumHeadless again (2/2).
14 06 2018 14:13:04.851:ERROR [launcher]: Cannot start ChromiumHeadless
[0614/141304.844602:ERROR:zygote_host_impl_linux.cc(88)] Running as root without --no-sandbox is not supported. See https://crbug.com/638180.

14 06 2018 14:13:04.851:ERROR [launcher]: ChromiumHeadless stdout:
14 06 2018 14:13:04.852:ERROR [launcher]: ChromiumHeadless stderr: [0614/141304.844602:ERROR:zygote_host_impl_linux.cc(88)] Running as root without --no-sandbox is not supported. See https://crbug.com/638180.

14 06 2018 14:13:04.853:ERROR [launcher]: ChromiumHeadless failed 2 times (cannot start). Giving up.
ERROR: Job failed: exit code 1