updated docker build badge
updated docker build badge

I changed the url so github requests a new image.
The build works.
https://hub.docker.com/r/mariobehling/loklak/builds/
singhpratyush/loklak_server,shivenmian/loklak_server,shivenmian/loklak_server,loklak/loklak_server,loklak/loklak_server,singhpratyush/loklak_server,singhpratyush/loklak_server,loklak/loklak_server,shivenmian/loklak_server,shivenmian/loklak_server,shivenmian/loklak_server,loklak/loklak_server,singhpratyush/loklak_server,loklak/loklak_server,loklak/loklak_server,singhpratyush/loklak_server,shivenmian/loklak_server,loklak/loklak_server,shivenmian/loklak_server,singhpratyush/loklak_server,singhpratyush/loklak_server