Ensure relative redirects

When the container port :80 is exposed as :8080 on the host,
nginx redirects to http://localhost:80/login.pl with a relative
path, instead of http://localhost:8080/login.pl; the container
isn't bound to :80, so that request fails...

with-proxy/nginx.conf

@@ -51,7 +51,7 @@ http {
       }
 
       location = / {
-         return 301 /login.pl;
+         return 301 login.pl;
       }
 
       # JS & CSS