Change Heroku button repo.

README.md

@@ -47,7 +47,7 @@ See [installation docs](https://listmonk.app/docs/installation).
 __________________
 
 ### Heroku 
-[![Deploy](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy?template=https://github.com/knadh/listmonk-heroku)
+[![Deploy](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy?template=https://github.com/knadh/listmonk-heroku-deploy)
 
 
 ## Developers