Show SKU on cart and checkout pages in Woocommerce 3

add_filter( 'woocommerce_cart_item_name', 'showing_sku_in_cart_items', 99, 3 );
function showing_sku_in_cart_items( $item_name, $cart_item, $cart_item_key  ) {
    // The WC_Product object
    $product = $cart_item['data'];
    // Get the  SKU
    $sku = $product->get_sku();

    // When sku doesn't exist
    if(empty($sku)) return $item_name;

    // Add the sku
    $item_name .= '<br><small class="product-sku">' . __( "SKU: ", "woocommerce") . $sku . '</small>';

    return $item_name;
}