link featured image to post

I am using the Jupiter theme (child theme) and instead of linking the featured image of a blog-post to lightbox I would like to link it straight to the post.

I have tried adding this to the child-themes functions php:

add_filter( ‘post_thumbnail_html’, ‘my_post_image_html’, 10, 3 );

function my_post_image_html( $html, $post_id, $post_image_id ) {
$html = ‘‘ . $html . ‘‘;
return $html;
}

as adviced in this article: http://codex.wordpress.org/Function_Reference/the_post_thumbnail
But no change.

URL: http://kalas.mdont.se/?cat=1
Please advice