Bump to Dockerspawner 0.4.

(c) Copyright IBM Corp. 2016

Author: Justin Tyberg

Dockerfile.jupyterhub

@@ -6,7 +6,7 @@ FROM jupyterhub/jupyterhub-onbuild:0.6.1
 RUN /opt/conda/bin/pip install \
     jupyterhub==0.6.* \
     oauthenticator==0.4.* \
-    dockerspawner==0.3.*
+    dockerspawner==0.4.*
 
 # Copy TLS certificate and key
 ENV SSL_CERT /srv/jupyterhub/secrets/jupyterhub.crt