Pages and Menu routing in Instagram Block (drupal-8)

new.instagram_block.module

function instagram_block_menu() {

  $items['admin/config/content/instagram_block'] = array(
    'title' => 'Instagram Block',
    'description' => 'Configuration page for Instagram Block.',
    'router_name' => 'instagram_block_admin_config_form',
  );

  return $items;
}

old.instagram_block.module

function instagram_block_menu() {

  $items['admin/config/content/instagram_block'] = array(
    'title' => 'Instagram Block',
    'description' => 'Configuration page for Instagram Block.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('instagram_block_admin_settings'),
    'access arguments' => array('administer site configuration'),
    'file' => 'instagram_block.admin.inc',
  );

  return $items;
}