remove PropertyWebBuilder demo link (error 503)

- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/2266

README.md

@@ -689,7 +689,7 @@ _Related: [Blogging Platforms](#blogging-platforms), [Static Site Generators](#s
 - [Pico](https://picocms.org/) - Stupidly simple, blazing fast, flat file CMS. ([Source Code](https://github.com/picocms/Pico)) `MIT` `PHP`
 - [Pimcore](https://www.pimcore.org/) - Multi-Channel Experience and Engagement Management Platform. ([Source Code](https://github.com/pimcore/pimcore)) `GPL-3.0-or-later` `PHP`
 - [Plone](https://plone.org/) - Powerful open-source CMS system. ([Source Code](https://github.com/plone)) `ZPL-2.0` `Python`
-- [PropertyWebBuilder](https://propertywebbuilder.com) - Ultimate Ruby on Rails engine for creating real estate websites. ([Demo](https://propertywebbuilder.herokuapp.com), [Source Code](https://github.com/etewiah/property_web_builder)) `MIT` `Ruby`
+- [PropertyWebBuilder](https://propertywebbuilder.com) - Ultimate Ruby on Rails engine for creating real estate websites. ([Source Code](https://github.com/etewiah/property_web_builder)) `MIT` `Ruby`
 - [Publify](https://publify.github.io/) - Simple but full featured web publishing software. ([Source Code](https://github.com/publify/publify)) `MIT` `Ruby`
 - [Rapido](https://framagit.org/InfoLibre/rapido) - Create your website with Rapido. Edit, publish and share collaborative content. `AGPL-3.0` `Go`
 - [REDAXO](https://www.redaxo.org) - Simple, flexible and useful content management system (documentation only available in German). ([Source Code](https://github.com/redaxo/redaxo)) `MIT` `PHP`