Do not pass host config options as start keyword args.

* Docker 1.12+ does not support host config options at container start.

(c) Copyright IBM Corp. 2016

Author: Justin Tyberg

jupyterhub_config.py

@@ -27,7 +27,6 @@
 c.DockerSpawner.network_name = network_name
 # Pass the network name as argument to spawned containers
 c.DockerSpawner.extra_host_config = { 'network_mode': network_name }
-c.DockerSpawner.extra_start_kwargs = { 'network_mode': network_name }
 # Explicitly set notebook directory because we'll be mounting a host volume to
 # it.  Most jupyter/docker-stacks *-notebook images run the Notebook server as
 # user `jovyan`, and set the notebook directory to `/home/jovyan/work`.