Causes exception

Error: Call to undefined function trilingslashit …
… /wp-content/plugins/spiritual-gifts-test/spiritualgiftssurvey.php”, line 58, in mvspg_spiritual_gifts_survey::mvspg_saveformemailsurveynotif
$url = trilingslashit(admin_url()) . ‘admin.php?page=spiritual_gifts_edit_menu’;