[gnome-calculator] Fix deprecatation using Gtk.Widget.font_desc

[Robert Ancell <rancell src gnome org>]

commit acbe28679670319a55e4af7b5e09e62376b0ab86
Author: Robert Ancell <robert ancell canonical com>
Date:   Tue Oct 15 10:39:13 2013 +1300

    Fix deprecatation using Gtk.Widget.font_desc

 src/math-display.vala |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/math-display.vala b/src/math-display.vala
index d366474..463ec78 100644
--- a/src/math-display.vala
+++ b/src/math-display.vala
@@ -39,9 +39,9 @@ public class MathDisplay : Gtk.Viewport
         /*text_view.set_right_margin (6);*/
         text_view.set_justification (Gtk.Justification.RIGHT);
         text_view.ensure_style ();
-        var font_desc = text_view.get_style ().font_desc.copy ();
+        var font_desc = text_view.get_style_context ().get_font (Gtk.StateFlags.NORMAL);
         font_desc.set_size (16 * Pango.SCALE);
-        text_view.modify_font (font_desc);
+        text_view.override_font (font_desc);
         text_view.set_name ("displayitem");
         text_view.get_accessible ().set_role (Atk.Role.EDITBAR);
         //FIXME:<property name="AtkObject::accessible-description" translatable="yes" comments="Accessible 
description for the area in which results are displayed">Result Region</property>