Removed demo link from Mailu entry (#2663)

The demo link leads to an empty wiki which is publicly editable
Signed-off-by: Akashdeep Dhar <akashdeep.dhar@gmail.com>
Co-authored-by: nodiscc <nodiscc@gmail.com>

README.md

@@ -243,7 +243,7 @@ _Simple deployment of a mail server, e.g. for inexperienced or impatient admins.
 - [Maddy Mail Server](https://github.com/foxcpp/maddy) - All-in-one mail server that implements SMTP (both MTA and MX) and IMAP. Replaces Postfix, Dovecot, OpenDKIM, OpenSPF, OpenDMARC with single daemon. `GPL-3.0` `Go`
 - [Mail-in-a-Box](https://mailinabox.email/) - Turns any Ubuntu server into a fully functional mail server with one command. ([Source Code](https://github.com/mail-in-a-box/mailinabox)) `CC0-1.0` `Shell`
 - [Mailcow](https://mailcow.email/) - Mail server suite based on Dovecot, Postfix and other open source software, that provides a modern Web UI for administration. ([Source Code](https://github.com/mailcow/mailcow-dockerized)) `GPL-2.0` `Docker/PHP`
-- [Mailu](https://mailu.io/) - Mailu is a simple yet full-featured mail server as a set of Docker images. ([Demo](https://github.com/Mailu/Mailu/wiki/Demo-server), [Source Code](https://github.com/Mailu/Mailu)) `MIT` `Docker/Python`
+- [Mailu](https://mailu.io/) - Mailu is a simple yet full-featured mail server as a set of Docker images. ([Source Code](https://github.com/Mailu/Mailu)) `MIT` `Docker/Python`
 - [Modoboa](https://modoboa.org/en/) - Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface. ([Source Code](https://github.com/modoboa/modoboa)) `ISC` `Python`
 - [Ptorx](https://github.com/xyfir/ptorx) - Email privacy. Anonymously send and receive with alias forwarding. `GPL-3.0` `Nodejs`
 - [Qmailtoaster](http://www.qmailtoaster.com/) - Stable, full-featured, easy-to-install mail server based on qmail. ([Source Code](https://github.com/QMailToaster/)) `Multiple` `Linux`