[gegl] docs: replace cat with include for compatibility

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

commit 9d04124916a1544f3bd8f8aff95fb7c7f0db2dc4
Author: John <jtm home gmail com>
Date:   Tue Jul 14 21:02:48 2020 +0100

    docs: replace cat with include for compatibility

 docs/hello-world.txt.in | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/docs/hello-world.txt.in b/docs/hello-world.txt.in
index a99327cfb..9f99d7376 100644
--- a/docs/hello-world.txt.in
+++ b/docs/hello-world.txt.in
@@ -1,5 +1,5 @@
 Hello world
-^^^^^^^^^^^
+-----------
 The following is a small sample GEGL application that animates a zoom on a
 mandelbrot fractal. compile it with:
 
@@ -10,5 +10,5 @@ link:http://git.gnome.org/browse/gegl/tree/examples/[examples subdir of the GEGL
 distribution].
 
 ---------------------------
-sys::[cat @top_srcdir@/examples/hello-world.c]
+include::@top_srcdir@/examples/hello-world.c[]
 ---------------------------