Retina JS not working

I intend to develop a Retina ready theme. I uploaded retina.min.js on my theme folder:

http://riehling.mrcoolblog.com/wp-content/themes/riehling/js/retina.min.js

In my functions.php, I've added the following code:

add_action( 'wp_enqueue_scripts', 'retina_support_enqueue_scripts' );
function retina_support_enqueue_scripts() {
    wp_enqueue_script( 'retina_min_js', get_template_directory_uri() . '/js/retina.min.js', null, '', true );
}

add_filter( 'wp_generate_attachment_metadata', 'retina_support_attachment_meta', 10, 2 );
function retina_support_attachment_meta( $metadata, $attachment_id ) {
    foreach ( $metadata as $key = $value ) {
        if ( is_array( $value ) ) {
            foreach ( $value as $image = $attr ) {
                if ( is_array( $attr ) )
                    retina_support_create_images( get_attached_file( $attachment_id ), $attr['width'], $attr['height'], true );
            }
        }
    }

    return $metadata;
}

function retina_support_create_images( $file, $width, $height, $crop = false ) {
    if ( $width || $height ) {
        $resized_file = wp_get_image_editor( $file );
        if ( ! is_wp_error( $resized_file ) ) {
            $filename = $resized_file-generate_filename( $width . 'x' . $height . '@2x' ); 
            $resized_file-resize( $width * 2, $height * 2, $crop );
            $resized_file-save( $filename );

            $info = $resized_file-get_size();

            return array(
                'file' = wp_basename( $filename ),
                'width' = $info['width'],
                'height' = $info['height'],
            );
        }
    }
    return false;
}

add_filter( 'delete_attachment', 'delete_retina_support_images' );
function delete_retina_support_images( $attachment_id ) {
    $meta = wp_get_attachment_metadata( $attachment_id );
    $upload_dir = wp_upload_dir();
    $path = pathinfo( $meta['file'] );
    foreach ( $meta as $key = $value ) {
        if ( 'sizes' === $key ) {
            foreach ( $value as $sizes = $size ) {
                $original_filename = $upload_dir['basedir'] . '/' . $path['dirname'] . '/' . $size['file'];
                $retina_filename = substr_replace( $original_filename, '@2x.', strrpos( $original_filename, '.' ), strlen( '.' ) );
                if ( file_exists( $retina_filename ) )
                    unlink( $retina_filename );
            }
        }
    }
}

It does create a @2x file (although I'm quite sure it stretches thumbnails instead of working with the source file, which is wide enough).

However, the image is not being handled by the Retina JS script:

http://riehling.mrcoolblog.com/projets/scenographie/test-retina/

I'm using ?php the_post_thumbnail( 'medium' ); ? to display the image and the output looks like this:

img width="236" height="310" src="http://riehling.mrcoolblog.com/wp-content/uploads/f2-236x310.jpg" class="attachment-medium size-medium wp-post-image" alt="Tiger" srcset="http://riehling.mrcoolblog.com/wp-content/uploads/f2-236x310.jpg 236w, http://riehling.mrcoolblog.com/wp-content/uploads/f2-768x1009.jpg 768w, http://riehling.mrcoolblog.com/wp-content/uploads/f2-472x620.jpg 472w, http://riehling.mrcoolblog.com/wp-content/uploads/f2.jpg 944w" sizes="(max-width: 236px) 100vw, 236px"