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>
diff --git a/shiny/widget/flex/flex_test.go b/shiny/widget/flex/flex_test.go
index 08aad08..85cc29b 100644
--- a/shiny/widget/flex/flex_test.go
+++ b/shiny/widget/flex/flex_test.go
@@ -382,7 +382,7 @@
 	for testNum, test := range layoutTests {
 		var children []node.Node
 		for i, sz := range test.measured {
-			n := widget.NewUniform(colors[i], unit.Pixels(sz[0]), unit.Pixels(sz[1]))
+			n := widget.NewSizer(unit.Pixels(sz[0]), unit.Pixels(sz[1]), widget.NewUniform(colors[i], nil))
 			if test.layoutData != nil {
 				n.LayoutData = test.layoutData[i]
 			}