Use the short product description instead of description (WooCommerce pre-3.0)

functions.php

<?php

function lw_woocommerce_gpf_description( $description, $product_id, $variation_id = null ) {
    global $post;
    if ( ! is_null( $variation_id ) ) {
        $ID = $variation_id;
    } else {
        $ID = $product_id;
    }
    $save_post = $post;
    $post = get_post( $ID );
    if ( ! empty( $post->post_parent ) ) {
        $post = get_post( $post->post_parent );
    }
    setup_postdata( $post );
    $excerpt = get_the_excerpt();
    $post = $save_post;
    return $excerpt;
}
add_filter( 'woocommerce_gpf_description', 'lw_woocommerce_gpf_description', 10, 3 );