Bump jupyterlab_server dependency.

setup.py

@@ -134,7 +134,7 @@ setup_args = dict(
 setup_args['install_requires'] = [
     'notebook>=4.3.1',
     'tornado<6',
-    'jupyterlab_server>=0.3.2,<0.4.0'
+    'jupyterlab_server>=0.3.3,<0.4.0'
 ]
 
 setup_args['extras_require'] = {