chore(docs): Remove broken docker deploy button (fossasia#6561)

Author: Swap76

Diff for: README.md

@@ -51,9 +51,9 @@ The Open Event Server can be easily deployed on a variety of platforms. Detailed
 1. [Deployment on Heroku](/docs/installation/heroku.md)
 
 
-One-click Heroku and Docker deployments are also available:
+One-click Heroku deployment is also available:
 
-[![Deploy to Docker Cloud](https://files.cloud.docker.com/images/deploy-to-dockercloud.svg)](https://cloud.docker.com/stack/deploy/?repo=https://github.com/fossasia/open-event-server)  [![Deploy](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy)
+[![Deploy](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy)
 
 
 ## Technology Stack