Docker: Don't show a warning for unset PORT_WORDPRESS variable. (#11584)

We default to `80` elsewhere. Default to `80` everywhere.

Author: mdawaffe

docker/docker-compose.yml

@@ -83,4 +83,4 @@ services:
       - default.env
       - .env
     environment:
-      - HOST_PORT=${PORT_WORDPRESS}
+      - HOST_PORT=${PORT_WORDPRESS:-80}