Image URL modified in README.md to work in Docker Hub

Author: jkarlosb

README.md

@@ -1,7 +1,7 @@
 # git-server-docker
 A lightweight Git Server Docker image built with Alpine Linux. Available on [GitHub](https://github.com/jkarlosb/git-server-docker) and [Docker Hub](https://hub.docker.com/r/jkarlos/git-server-docker/)
 
-!["image git server docker" "git server docker"](https://github.com/jkarlosb/git-server-docker/blob/master/git-server-docker.jpg)
+!["image git server docker" "git server docker"](https://raw.githubusercontent.com/jkarlosb/git-server-docker/master/git-server-docker.jpg)
 
 ### Basic Usage