[gtk] gtk-demo: Reinstate flat menu buttons

[Matthias Clasen <matthiasc src gnome org>]

commit d0137ef62745ff29c90bec05320bd9cf098c2218
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue May 21 22:39:50 2019 +0000

    gtk-demo: Reinstate flat menu buttons

 demos/gtk-demo/listbox.ui | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/demos/gtk-demo/listbox.ui b/demos/gtk-demo/listbox.ui
index 565f959568..5ac7f7ecfa 100644
--- a/demos/gtk-demo/listbox.ui
+++ b/demos/gtk-demo/listbox.ui
@@ -172,6 +172,7 @@
                     <property name="can-focus">1</property>
                     <property name="receives-default">1</property>
                     <property name="popup">menu1</property>
+                    <property name="relief">none</property>
                     <property name="label" translatable="yes">More...</property>
                   </object>
                 </child>