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

commit spouliot/Touch.Unit@055659f10a
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.

external/Touch.Unit

@@ -1 +1 @@
-Subproject commit 708348b0c1a7c60c8e00e80df2a119b51ca2b85f
+Subproject commit 055659f10af409c7e369ee3372bd3f4b1a99fd2c