Update citadel link

README.md

@@ -1022,7 +1022,7 @@ Games, game servers and control panels.
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 - [BlueMind](https://www.bluemind.net/en/) - Groupware with email, calendar, addressbooks, exchange active sync, exchange MAPI protocol support. ([Source Code](https://forge.bluemind.net/stash/projects/BM/repos/bluemind-public/browse)) `AGPL-3.0` `Java`
-- [Citadel](https://www.citadel.org/doku.php) - Groupware including email, calendar/scheduling, address books, forums, mailing lists, IM, wiki and blog engines, RSS aggregation and more. ([Source Code](https://www.citadel.org/source.html)) `GPL-3.0` `C`
+- [Citadel](https://www.citadel.org/) - Groupware including email, calendar/scheduling, address books, forums, mailing lists, IM, wiki and blog engines, RSS aggregation and more. ([Source Code](https://www.citadel.org/source.html)) `GPL-3.0` `C`
 - [Corteza](https://cortezaproject.org) - CRM including a unified workspace, enterprise messaging and a low code environment for rapidly and securely delivering records-based management solutions. ([Demo](https://latest.cortezaproject.org), [Source Code](https://github.com/cortezaproject/corteza-server)) `Apache-2.0` `Go`
 - [Cozy Cloud](https://cozy.io) - Personal cloud where you can manage and sync your contact, files and calendars, and manage your budget with an app store full of community contributions. ([Source Code](https://github.com/cozy)) `GPL-3.0` `Nodejs`
 - [egroupware](https://www.egroupware.org/) - Software suite including calendars, address books, notepad, project management tools, client relationship management tools (CRM), knowledge management tools, a wiki and a CMS. ([Source Code](https://github.com/EGroupware/egroupware)) `GPL-2.0` `PHP`