remove solo: source code is gone, website changed owner

README.md

@@ -209,7 +209,6 @@ See also [Static Site Generators](#static-site-generators), [Content Management
 - [Plume](https://joinplu.me/) - Federated blogging engine, based on ActivityPub. ([Source Code](https://github.com/Plume-org/Plume)) `AGPL-3.0` `Rust`
 - [PluXml](http://www.pluxml.org/) - XML-based blog/CMS platform. ([Source Code](https://github.com/pluxml/PluXml)) `GPL-1.0` `PHP`
 - [Postleaf](https://www.postleaf.org/) - Open source blogging platform with inline editing, handlebar templates, and a beautiful user interface. ([Source Code](https://github.com/Postleaf/postleaf)) `MIT` `Nodejs`
-- [Solo](http://b3log.org/) - Blogging system written in Java, feel free to create your or your team own blog. ([Demo](http://88250.b3log.org/), [Source Code](https://github.com/b3log/solo)) `Apache-2.0` `Java`
 
 
 ## Bookmarks and Link Sharing