ot_remote_builtin_show_url: autofree context

Leak found with valgrind memcheck.

Signed-off-by: Simon McVittie <smcv@debian.org>

Closes: #556
Approved by: cgwalters

src/ostree/ot-remote-builtin-show-url.c

@@ -32,7 +32,7 @@ static GOptionEntry option_entries[] = {
 gboolean
 ot_remote_builtin_show_url (int argc, char **argv, GCancellable *cancellable, GError **error)
 {
-  GOptionContext *context;
+  g_autoptr(GOptionContext) context = NULL;
   glnx_unref_object OstreeRepo *repo = NULL;
   const char *remote_name;
   g_autofree char *remote_url = NULL;