make redis host configurable through env variable

docker/ddns/Dockerfile

@@ -8,4 +8,4 @@ RUN go-wrapper install    # "go install -v ."
 
 ENV GIN_MODE release
 
-CMD /go/bin/ddns --domain=${DDNS_DOMAIN} --soa_fqdn=${DDNS_SOA_DOMAIN} --redis=redis:6379 web
+CMD /go/bin/ddns --domain=${DDNS_DOMAIN} --soa_fqdn=${DDNS_SOA_DOMAIN} --redis=${DDNS_REDIS_HOST}

docker/docker-compose.yml

@@ -10,7 +10,8 @@ services:
       - redis
     environment:
       DDNS_DOMAIN: d.example.net
-      DDNS_SOA_DOMAIN: soa.example.net
+      DDNS_SOA_DOMAIN: ns.example.net
+      DDNS_REDIS_HOST: redis:6379
 
   powerdns:
     restart: unless-stopped