Support For Twitch

I ran into a request for Twitch to be supported. (Still can't get past this "limit" on forking projects to add things.)

<?php

namespace Drupal\social_link_field\Plugin\SocialLinkField\Platform;

use Drupal\social_link_field\PlatformBase;

/**
 * Provides 'twitch' platform.
 *
 * @SocialLinkFieldPlatform(
 *   id = "twitch",
 *   name = @Translation("Twitch"),
 *   icon = "fa-twitch",
 *   urlPrefix = "https://www.twitch.tv/",
 * )
 */
class Twitch extends PlatformBase {}