Use https:// prefix for redis.io to fix failing build of Url Checker (redirect is marked as failure)

README.md

 * [MailCatcher](https://github.com/sj26/mailcatcher) - A web tool for capturing and viewing emails.
 * [Cachet](https://github.com/cachethq/cachet) - The open source status page system.
 * [phpBeanstalkdAdmin](https://github.com/mnapoli/phpBeanstalkdAdmin) - Monitoring and administration interface for Beanstalkd.
-* [phpRedisAdmin](https://github.com/ErikDubbelboer/phpRedisAdmin) - A simple web interface to manage [Redis](http://redis.io/) databases.
+* [phpRedisAdmin](https://github.com/ErikDubbelboer/phpRedisAdmin) - A simple web interface to manage [Redis](https://redis.io/) databases.
 * [phpPgAdmin](https://github.com/phppgadmin/phppgadmin) - A web-based administration tool for PostgreSQL.
 * [phpMyAdmin](https://github.com/phpmyadmin/phpmyadmin) - A web interface for MySQL/MariaDB.
 * [Adminer](https://www.adminer.org/) - Database management in a single PHP file.