bump required tornado

Author: blink1073

setup.py

@@ -65,7 +65,7 @@ def run(self):
         'ipython>=7.23.1',
         'traitlets>=5.1.0,<6.0',
         'jupyter_client<8.0',
-        'tornado>=4.2,<7.0',
+        'tornado>=5.0,<7.0',
         'matplotlib-inline>=0.1.0,<0.2.0',
         'appnope;platform_system=="Darwin"',
         'psutil',