Update docker.md

Author: qasim-at-tci

user/docker.md

@@ -185,7 +185,7 @@ env:
 
 before_install:
   - sudo rm /usr/local/bin/docker-compose
-  - curl -L https://github.com/docker/compose/releases/download/${DOCKER_COMPOSE_VERSION}/docker-compose-`uname -s`-`uname -m` > docker-compose
+  - curl -L https://github.com/docker/compose/releases/download/v${DOCKER_COMPOSE_VERSION}/docker-compose-`uname -s`-`uname -m` > docker-compose
   - chmod +x docker-compose
   - sudo mv docker-compose /usr/local/bin
 ```