Added jupyter-server-proxy to install_requires

Need jupyter-server-proxy to setup websocket connections on JupyterHub and Binder.

Author: jcoady

setup.py

@@ -18,7 +18,7 @@
 
 import versioneer
 
-install_requires = ['jupyter', 'numpy', 'ipykernel',
+install_requires = ['jupyter', 'jupyter-server-proxy', 'numpy', 'ipykernel',
                     'autobahn>=18.8.2']
 
 if sys.version_info.major == 3 and sys.version_info.minor >= 5: