Bump Touch.Unit to get a hopefully helpful debug message. (#2084)

commit xamarin/Touch.Unit@055659f
Author: Rolf Bjarne Kvinge <rolf@xamarin.com>
Date:   Wed May 10 16:23:43 2017 +0200

    [TouchRunner] Print something before exiting. (#45)

    This might help us narrow down https://bugzilla.xamarin.com/show_bug.cgi?id=56162.