[gnome-robots] Fixs prefs dialog not modal

[Michael Catanzaro <mcatanzaro src gnome org>]

commit c9485d432d66112dba8698590c90ec7b54a1e67b
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Fri Jan 3 21:14:43 2020 -0600

    Fixs prefs dialog not modal

 src/properties.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/properties.c b/src/properties.c
index d3fa1d4..38402fa 100644
--- a/src/properties.c
+++ b/src/properties.c
@@ -390,7 +390,7 @@ show_properties_dialog (void)
 
   propbox = gtk_dialog_new_with_buttons (_("Preferences"),
                                         GTK_WINDOW (window),
-                                        GTK_DIALOG_USE_HEADER_BAR,
+                                        GTK_DIALOG_USE_HEADER_BAR | GTK_DIALOG_MODAL,
                                         NULL,
                                         NULL);
   gtk_container_set_border_width (GTK_CONTAINER (propbox), 5);