gistfile1.php

add_filter( 'get_custom_logo', 'onepress_child_custom_logo' );

function onepress_child_custom_logo() {
    $custom_logo_id = get_theme_mod( 'custom_logo' );
    $html = sprintf( '<a target="_blank" href="%1$s" class="custom-logo-link" rel="home" itemprop="url">%2$s</a>',
            esc_url( home_url( '/' ) ),
            wp_get_attachment_image( $custom_logo_id, 'full', false, array(
                'class'    => 'custom-logo',
            ) )
        );
    return $html;   
}