Adding a filter for “image” meta name.

Hello,

The plugin is excellent. Could you consider adding a filter for the “image” meta name instead of hard-coding it?

https://plugins.trac.ww.wp.xz.cn/browser/og/trunk/includes/iworks/class-iworks-opengraph.php#L802

This line

$image_id                = intval( get_term_meta( $obj->term_id, 'image', true ) );

It would be great if it had a filter, perhaps something like this

            $image_field            = apply_filters( 'og_term_thumbnail_meta', 'image', $obj );

            $image_id                = intval( get_term_meta( $obj->term_id, $image_field, true ) );

Thanks.