[pybliographer] ui: Fix use of gtk3 in a gtk2 application

[Germán Poo-Caamaño <gpoo src gnome org>]

commit c374a7c8adebd0af0d20b075cf111d41f2b6464f
Author: Germán Poo-Caamaño <gpoo gnome org>
Date:   Mon Mar 26 00:36:07 2018 -0300

    ui: Fix use of gtk3 in a gtk2 application

 Pyblio/GnomeUI/Utils.py |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/Pyblio/GnomeUI/Utils.py b/Pyblio/GnomeUI/Utils.py
index 9817089..74b567b 100644
--- a/Pyblio/GnomeUI/Utils.py
+++ b/Pyblio/GnomeUI/Utils.py
@@ -229,10 +229,10 @@ def error_dialog_s(parent, primary, secondary=None):
 
 
 def warning_dialog_s(parent, primary, secondary=None):
-    dialog = Gtk.MessageDialog(parent,
-                               Gtk.DialogFlags.MODAL | Gtk.DialogFlags.DESTROY_WITH_PARENT,
-                               Gtk.MessageType.WARNING,
-                               Gtk.ButtonsType.CLOSE, primary)
+    dialog = gtk.MessageDialog(parent,
+                               gtk.DIALOG_MODAL | gtk.DIALOG_DESTROY_WITH_PARENT,
+                               gtk.MESSAGE_WARNING,
+                               gtk.BUTTONS_CLOSE, primary)
     if secondary:
         dialog.format_secondary_text(secondary)
     dialog.run()