blacklist tornado versions that throw 'Already reading' error

setup.py

@@ -132,7 +132,7 @@ setup_args = dict(
 
 setup_args['install_requires'] = [
     'notebook>=4.3.1',
-    'tornado>=6.0.3',
+    'tornado!=6.0.0, !=6.0.1, !=6.0.2',
     'jupyterlab_server~=1.0.0rc0'
 ]