update deps

setup.py

@@ -156,8 +156,7 @@ setup_args = dict(
 setup_args['install_requires'] = [
     'ipython',
     'tornado!=6.0.0, !=6.0.1, !=6.0.2',
-    'jupyterlab_server>=2.0.0b0',
-    'jupyter_server>=1.0.0rc5',
+    'jupyterlab_server~=2.0.0b1',
     'nbclassic>=0.2.0rc3',
     'jinja2>=2.10'
 ]