[libgit2-glib] Fix warning about missing cast in walk example

[Jesse van den Kieboom <jessevdk src gnome org>]

commit 68abf7450d41b51485e40c318537858e72839e51
Author: Jesse van den Kieboom <jessevdk gmail com>
Date:   Wed Sep 10 09:49:20 2014 +0200

    Fix warning about missing cast in walk example

 examples/walk.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/examples/walk.c b/examples/walk.c
index b9f5ada..6327ada 100644
--- a/examples/walk.c
+++ b/examples/walk.c
@@ -57,7 +57,7 @@ diff_print_cb (GgitDiffDelta    *delta,
        gchar *s;
 
        content = ggit_diff_line_get_content (line, &len);
-       s = g_strndup (content, len);
+       s = g_strndup ((const gchar *)content, len);
 
        g_print ("%s", s);
        g_free (s);