How to create a custom template for this custom post type?

I've created this custom post type.

/* custom post - traveller posts */ 
add_action( 'init', 'traveller' );
function traveller() {
  register_post_type( 'traveller',
    array(
      'labels' => array(
        'name' => __( 'Traveller_Posts' ),
        'singular_name' => __( 'Traveller_Post' )
      ),
        'public' => true,
        'has_archive' => true,
        'capability_type' => array("Traveller_Post", "Traveller_Posts"),
        'map_meta_cap' => true,
    )
  );
}

That creates a post type 'Traveller_posts'

Now I have to create a template for these 'Traveller_post'types.

• 
  

  So I created 'single-traveller.php' - Not working.

  
  


• 
  

  Then I created 'single-traveller_post.php' - also not working

  
  


• 
  

  Then I tried 'single-traveller_posts.php' - no luck again.

  
  

I put all these files into my child theme directory.

Why I am unable to get it works? What can I do to get it works?