Updated _docker-compose to the latest version (from 0.1.0 to 1.5.0). (#5215)

Also fixed formatting of markdown URL in README.

plugins/docker-compose/README.md

 # Docker-compose plugin for oh my zsh
 
-A copy of the completion script from the [docker-compose](1) git repo.
+A copy of the completion script from the [docker-compose](https://github.com/docker/compose/blob/master/contrib/completion/zsh/_docker-compose) git repo.
 
-[1]:[https://github.com/docker/compose/blob/master/contrib/completion/zsh/_docker-compose]