Fix the broken URL

It was not redirecting to the proper page

Signed-off-by: Przemek Hejman <przemyslaw.hejman@gmail.com>

Author: mieciu

docs/env.md

@@ -30,4 +30,4 @@ Protocol (tcp or udp), e.g. `DB_PORT_5432_TCP_PROTO=tcp`
 <b><i>name</i>\_NAME</b><br>
 Fully qualified container name, e.g. `DB_1_NAME=/myapp_web_1/myapp_db_1`
 
-[Docker links]: http://docs.docker.io/en/latest/use/port_redirection/#linking-a-container
+[Docker links]: http://docs.docker.com/userguide/dockerlinks/