Update .gitlab-ci.yml

1 job for master in 5 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
failed build #4777

00:00:05

 
Name Stage Failure
failed
build Build
 .gitlab-ci.yml | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
$ apt-get install tree
Reading package lists...
Building dependency tree...
Reading state information...
E: Unable to locate package tree
Cleaning up file based variables
ERROR: Job failed: exit code 1