[gegl] examples/hello-world.c: use gegl:display as comments indicate, not everyone has gegl:ff-save

[Øyvind Kolås <ok src gnome org>]

commit 08a0e525f62c44577d77ccc215504c4b54115f30
Author: Øyvind Kolås <pippin gimp org>
Date:   Thu Oct 26 21:33:28 2017 +0200

    examples/hello-world.c: use gegl:display as comments indicate, not everyone has gegl:ff-save

 examples/hello-world.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/examples/hello-world.c b/examples/hello-world.c
index 9890287..a5d162b 100644
--- a/examples/hello-world.c
+++ b/examples/hello-world.c
@@ -45,7 +45,7 @@ This is the graph we're going to construct:
 */
 
     /*< The image nodes representing operations we want to perform */
-    GeglNode *display    = gegl_node_create_child (gegl, "gegl:ff-save");
+    GeglNode *display    = gegl_node_create_child (gegl, "gegl:display");
     GeglNode *crop       = gegl_node_new_child (gegl,
                                  "operation", "gegl:crop",
                                  "width", 512.0,