switch restart to string

Signed-off-by: Benoît Stahl <from+github@b5.pm>

prometheus-grafana/docker-compose.yml

@@ -7,8 +7,7 @@ services:
       - '--config.file=/etc/prometheus/prometheus.yml'
     ports:
       - 9090:9090
-    restart:
-      - unless-stopped
+    restart: unless-stopped
     volumes:
       - ./prometheus:/etc/prometheus
       - prom_data:/prometheus
@@ -17,8 +16,7 @@ services:
     container_name: grafana
     ports:
       - 3000:3000
-    restart:
-      - unless-stopped
+    restart: unless-stopped
     environment:
       - GF_SECURITY_ADMIN_USER=admin
       - GF_SECURITY_ADMIN_PASSWORD=grafana