[gegl] configure: depend on babl 0.1.56

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 7ab21c10084984fe8b8beebb83561c6b28766cf1
Author: Øyvind Kolås <pippin gimp org>
Date:   Tue Aug 14 18:32:32 2018 +0200

    configure: depend on babl 0.1.56

 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/configure.ac b/configure.ac
index 5aacd1eb6..db11350ec 100644
--- a/configure.ac
+++ b/configure.ac
@@ -37,7 +37,7 @@ m4_define([gegl_stable],
 m4_define([gimp_full_name], [Generic Graphical Library])
 
 # required versions of external libraries
-m4_define([babl_required_version], [0.1.54])
+m4_define([babl_required_version], [0.1.56])
 m4_define([cairo_required_version], [1.12.2])
 m4_define([exiv2_required_version], [0.25])
 m4_define([gdk_pixbuf_required_version], [2.32.0])