dnet: downgrade urwid version
upgrading urwid to 2.2.0 breaks dnet in two ways:
* ui is not visible unless the terminal is in focus
* the screen is not redrawing correctly- contains artifacts from previous draw.
it may have to do with this breaking change that was added to 2.2.0:
https://github.com/urwid/urwid/pull/541
but i am not sure yet, investigating.