Update jupyterlab_server to 2.0.0rc1

setup.py

@@ -145,7 +145,7 @@ setup_args['install_requires'] = [
     'ipython',
     'packaging',
     'tornado!=6.0.0, !=6.0.1, !=6.0.2',
-    'jupyterlab_server~=2.0.0rc0',
+    'jupyterlab_server~=2.0.0rc1',
     'jupyter_server~=1.0.1',
     'nbclassic~=0.2.0',
     'jinja2>=2.10'