scancel does not send signal to jupyterhub

### Bug description
usually, when I execute `scancel` jupyter_job_id, spawning is immediately stopped and I see that message on the browser too.
Now, the job is canceled (squeue is empty) but in the browser I still see `Your server is starting up.
You will be redirected automatically when it's ready for you.

#### Expected behaviour
spawning stops when scancel is executed.

### Your personal set up
- OS: CentOS7
- jupyterhub: 1.3.0
- batchspawner (SlurmSpawner): 1.1.0
- python: 3.6

is this related to the batchspawner or jupyterhub? for information, everything was working fine before the upgrade (jupyterhub and batchspawner).