[gegl] configure.ac: increase gtk+ version dependency to be >2.18

[Øyvind Kolås <ok src gnome org>]

commit 4ca513305894125e66e9848bc83f903b3b217a0d
Author: �yvind Kolås <pippin gimp org>
Date:   Sat Apr 3 00:21:00 2010 +0100

    configure.ac: increase gtk+ version dependency to be >2.18
    
    gtk_widget_get_allocation is used and was introduced in 2.18

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 70222d1..58c28b1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -39,7 +39,7 @@ m4_define([gimp_full_name], [Generic Graphical Library])
 # required versions of external libraries
 m4_define([babl_required_version], [0.1.2])
 m4_define([glib_required_version], [2.22.0])
-m4_define([gtk_required_version], [2.8.6])
+m4_define([gtk_required_version], [2.18.0])
 m4_define([lua_required_version], [5.1.0])
 m4_define([cairo_required_version], [0.0.0])
 m4_define([pango_required_version], [0.0.0])