message: docs: make deprecated version linkable
diff: @@ -5,7 +5,8 @@ As of release 1.3.0, Envoy will follow a
  The following features have been DEPRECATED and will be removed in the specified release cycle.
  -* Version 1.4.0
  +## Version 1.4.0
  +
  * Config option `statsd_local_udp_port` has been deprecated and has been replaced with
  `statsd_udp_ip_address`.
  * `HttpFilterConfigFactory` filter API has been deprecated in favor of `NamedHttpFilterConfigFactory`.
  