[gnome-sudoku/vala-port] Bump required GTK+ version to 3.13.0

[Parin Porecha <parinporecha src gnome org>]

commit 961847d5ca319be86f037378cc1ae71c69171940
Author: Parin Porecha <parinporecha gmail com>
Date:   Fri May 23 15:47:45 2014 +0530

    Bump required GTK+ version to 3.13.0
    
    3.13 adds support for RTL icons in GtkIconTheme.
    See https://bugzilla.gnome.org/show_bug.cgi?id=730598

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 5e66425..cf38407 100644
--- a/configure.ac
+++ b/configure.ac
@@ -15,7 +15,7 @@ dnl ###########################################################################
 dnl Dependencies
 dnl ###########################################################################
 
-GTK_REQUIRED=3.12.0
+GTK_REQUIRED=3.13.0
 
 PKG_CHECK_MODULES(GNOME_SUDOKU, [
   gio-2.0