remove snibox demo link (error 503)

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

README.md

@@ -1501,7 +1501,7 @@ A [pastebin](https://en.wikipedia.org/wiki/Pastebin) is a type of online content
 - [PurritoBin](https://github.com/PurritoBin/PurritoBin) - Ultra fast, minimalistic, encrypted command line paste-bin, where the server has no knowledge of the paste data. `ISC` `C++`
 - [rustypaste](https://github.com/orhun/rustypaste) - A minimal file upload/pastebin service. `MIT` `Rust`
 - [SharpPaste](https://github.com/phonicmouse/SharpPaste) - Cross-platform C# pastebin with client-side AES-256 encryption that just works. `MIT` `C#/NancyFX`
-- [Snibox](https://snibox.github.io/) - Code snippets manager with attractive tag-oriented interface. ([Demo](https://snibox-demo.herokuapp.com/), [Source Code](https://github.com/snibox/snibox)) `MIT` `Ruby`
+- [Snibox](https://snibox.github.io/) - Code snippets manager with attractive tag-oriented interface. ([Source Code](https://github.com/snibox/snibox)) `MIT` `Ruby`
 - [Snippet Box](https://github.com/pawelmalak/snippet-box) - Snippet Box is a simple self-hosted app for organizing your code snippets. It allows you to easily create, edit, browse and manage your snippets in various languages. `MIT` `Nodejs`
 - [snipt](https://github.com/nicksergeant/snipt) - Long-term memory for coders. Share and store code snippets. `MIT` `Python`
 - [SnyPy](https://snypy.com) - Open source on-prem code snippet manager. ([Demo](https://app.snypy.com), [Source Code](https://github.com/snypy)) `MIT` `Docker`