[latexila] MainWindow: don't use gtk_menu_popup() (deprecated)

[Sébastien Wilmet <swilmet src gnome org>]

commit a14aed958765f6f9f1fc0971f11bc2d6f03bef0f
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Thu Dec 14 15:50:13 2017 +0100

    MainWindow: don't use gtk_menu_popup() (deprecated)
    
    For the GtkNotebook tab label right-click menu.

 src/main_window.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/main_window.vala b/src/main_window.vala
index b6edd4d..b0a7e51 100644
--- a/src/main_window.vala
+++ b/src/main_window.vala
@@ -476,7 +476,7 @@ public class MainWindow : ApplicationWindow
         _documents_panel.right_click.connect ((event) =>
         {
             Gtk.Menu popup_menu = _ui_manager.get_widget ("/NotebookPopup") as Gtk.Menu;
-            popup_menu.popup (null, null, null, event.button, event.time);
+            popup_menu.popup_at_pointer (event);
         });
     }