Use jserver extension-loading branch

setup.py

@@ -154,7 +154,7 @@ setup_args['install_requires'] = [
     'tornado!=6.0.0, !=6.0.1, !=6.0.2',
     'jupyterlab_server@ git+https://github.com/datalayer-contrib/jupyterlab-server@jupyter_server',
     'jupyter_server@ git+https://github.com/Zsailer/jupyter-server.git@extension-loading',
-    'nbclassic@ git+https://github.com/datalayer-contrib/jupyter-notebook-classic@jupyter_server_master',
+    'nbclassic@ git+https://github.com/Zsailer/nbclassic@master',
     'jinja2>=2.10'
 ]