Exclude old events from WP_Query with date saved in a `meta_key`

I use the bellow template to display the first event from an ascendent list of custom post type events, created by a third party plugin. What I want is to exclude old events, displaying only the one actual, if we have one today, or the nearest. The event start date is saved in a meta_key with a value in the “Y-m-d” format (ex: 2017-10-27). How to accomplish this?

        'posts_per_page'    => 1,
        'meta_key'          => 'event_start_date',
        'order'             => 'ASC'

    $featured = new WP_Query($args);

    if ($featured->have_posts()): 
        while($featured->have_posts()): $featured->the_post();

            $featured_event_start = $post->event_start_date;
            $featured_event_end = $post->event_end_date;

            if (has_post_thumbnail()) : ?>


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