example/{kitchen,tabs,gophers}: update to use material.Palette

Update gioui.org/cmd while here.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

example/gophers/ui.go

@@ -72,8 +72,7 @@ type (
 
 func init() {
 	theme = material.NewTheme(gofont.Collection())
-	theme.Color.Text = rgb(0x333333)
-	theme.Color.Hint = rgb(0xbbbbbb)
+	theme.Palette.Fg = rgb(0x333333)
 }
 
 func newUI(fetchCommits func(string)) *UI {