Remove size attributes on thumbnails

// Remove thumbnail width and height dimensions that prevent fluid images in the_thumbnail
function remove_thumbnail_dimensions( $html )
{
    $html = preg_replace('/(width|height)=\"\d*\"\s/', "", $html);
    return $html;
}


add_filter('post_thumbnail_html', 'remove_thumbnail_dimensions', 10); // Remove width and height dynamic attributes to thumbnails
add_filter('image_send_to_editor', 'remove_thumbnail_dimensions', 10); // Remove width and height dynamic attributes to post images