Update docker-compose.yml to add 'dind' to 'Workspace' (#1869)

Add 'docker-in-docker' links end 'DOCKER_HOST' environment to 'workspace'.

docker-compose.yml

@@ -111,9 +111,12 @@ services:
       tty: true
       environment:
         - PHP_IDE_CONFIG=${PHP_IDE_CONFIG}
+        - DOCKER_HOST=tcp://docker-in-docker:2375
       networks:
         - frontend
         - backend
+      links:
+        - docker-in-docker
 
 ### PHP-FPM ##############################################
     php-fpm: