shiny/widget/flex: build fix for the test code.

The widget.NewUniform signature changed in
https://go-review.googlesource.com/#/c/24871/

Change-Id: I7713df75d3cff87fbb1130d0880ad8b2b61abd1a
Reviewed-on: https://go-review.googlesource.com/24920
Reviewed-by: David Symonds <dsymonds@golang.org>
1 file changed