Update .gitlab-ci.yml

1 job for master in 3 minutes and 48 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Test
failed #250
pages

00:03:48

 
Name Stage Failure
failed
pages Test
Traceback (most recent call last):
File "./m.css/documentation/doxygen.py", line 3697, in <module>
os.makedirs(state.doxyfile['OUTPUT_DIRECTORY'], exist_ok=True)
File "/usr/lib/python3.6/os.py", line 220, in makedirs
mkdir(name, mode)
FileNotFoundError: [Errno 2] No such file or directory: ''
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit status 1