README.md: (misc) Update URL

Author: simnalamburt

README.md

@@ -38,7 +38,7 @@ RACK_ENV=production bundle exec run
 *chat* is primarily distributed under the terms of both the [Apache License
 (Version 2.0)] and the [MIT license]. See [COPYRIGHT] for details.
 
-[Sample Image]: https://raw.githubusercontent.com/simnalamburt/i/master/chat/sample.png
+[Sample Image]: https://i.hyeon.me/chat/sample.png
 [Apache License (Version 2.0)]: LICENSE-APACHE
 [MIT license]: LICENSE-MIT
 [COPYRIGHT]: COPYRIGHT