[gdk-pixbuf] docs: Fix docs build error

[Bastien Nocera <hadess src gnome org>]

commit abd12802fdb1d092c7af11b9fe79217ac0dd0721
Author: Bastien Nocera <hadess hadess net>
Date:   Mon Dec 4 18:14:21 2017 +0100

    docs: Fix docs build error
    
    WARNING: Passed invalid keyword argument "html_images" in docs/reference/gdk-pixbuf/meson.build line 30.

 docs/reference/gdk-pixbuf/meson.build |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/docs/reference/gdk-pixbuf/meson.build b/docs/reference/gdk-pixbuf/meson.build
index b8d6f22..fcfcb0d 100644
--- a/docs/reference/gdk-pixbuf/meson.build
+++ b/docs/reference/gdk-pixbuf/meson.build
@@ -45,7 +45,7 @@ if get_option('with_docs')
                  '--extra-dir=@0@'.format(join_paths(glib_docpath, 'gobject')),
                  '--extra-dir=@0@'.format(join_paths(glib_docpath, 'gio')),
                ],
-               html_images: [
+               html_assets: [
                  'composite.png',
                ],
                content_files: [