use server branch py35

setup.py

@@ -142,7 +142,7 @@ setup_args['install_requires'] = [
     'tornado!=6.0.0, !=6.0.1, !=6.0.2',
     'jinja2>=2.10',
     'jupyterlab_server@ git+https://github.com/datalayer-contrib/jupyterlab-server@jupyter_server',
-    'jupyter_server@ git+https://github.com/jupyter/jupyter_server.git@master',
+    'jupyter_server@ git+https://github.com/datalayer-contrib/jupyter-server.git@py35',
     'nbclassic@ git+https://github.com/datalayer-contrib/jupyter-notebook-classic@jupyter_server_master',
 ]