.gitlab-ci.yml: a demo pipeline with allow_failure

see #27
4 jobs for demo/fail-a in 17 seconds (queued for 5 minutes and 58 seconds)
latest
Status Job ID Name Coverage
  Unit
passed #296663
unit

00:00:01

 
  Demo
passed #296664
demo

00:00:04

 
  Demo A
failed #296665
allowed to fail
demo_a

00:00:04

 
  Coverage
passed #296666
coverage

00:00:06

86.0%
 
Name Stage Failure
failed
demo_a Demo A
  demo/cal.should
files with
skip:
demo/requires.should
demo/unicode.should
src/should.py --retry will relaunch these tests.
Uploading artifacts...
should.xml: found 1 matching files
Uploading artifacts to coordinator... ok
id=296665 responseStatus=201 Created token=zFQ1mhKZ
ERROR: Job failed: exit status 1