Add uninstall script.

<?php

if (!defined('WP_UNINSTALL_PLUGIN'))

    exit();

$option_name = 'word_count_options';

if (is_multisite()) {

    $ms_sites = function_exists('get_sites') ? get_sites() : wp_get_sites();

    if (0 < sizeof($ms_sites)) {

        foreach ($ms_sites as $ms_site) {

            $blog_id = isset($ms_site['blog_id']) ?

                $ms_site['blog_id'] : $ms_site->blog_id;

            switch_to_blog($blog_id);

            delete_option($option_name);

        }

    }

    restore_current_blog();

} else {

    delete_option($option_name);

}