WP_Query custom post type query not showing the exact post type

I am new in WordPress. I have registered wp_query function through ‘custom post type UI’ and ‘Advanced custom fields’ plugin. And this is the code in the portfolio page.

<div id="tf-content">
<div class="container"><!-- Container -->
    <div class="row"><!-- Row -->
        <?php
            $args = array(
                'post-type' => 'portfolio'
            );
            $query = new WP_Query( $args );
        ?>

        <?php if($query -> have_posts() ) : while( $query -> have_posts() ) : $query -> the_post(); ?>

        <a href= "<?php the_permalink(); ?>">
            <div class="col-md-4 col-sm-12 col-lg-3 col-xl-2">
                <div class="post-block" style= "margin: 0;"> <!-- Post #1-->
                    <div class="post-detail" style= "padding: 0;">
                        <div class="img-wrap">
                            <?php the_post_thumbnail(); ?>
                        </div>
                    </div>
                </div>
            </div>
        </a>
        <?php endwhile; endif; wp_reset_postdata(); ?>

    </div><!-- end Row -->
</div><!-- End Container -->

I want this code to query all the ‘portfolio’ type custom post but I don’t know why this code queries with general post but not portfolio type post. Please give me a solution for this.

Thank you in advance.