Fix for https://github.com/jupyter/terminado/issues/62
Fix for https://github.com/jupyter/terminado/issues/62

Jupyter brings in latest tornado version 6.0.1 and it breaks Jupyter Terminal due to removing
of gen.Task in earlier version, https://www.tornadoweb.org/en/stable/releases/v6.0.0.html

takluyver/terminado,takluyver/terminado