doc: add link to `net.Server` in tls.md

PR-URL: https://github.com/nodejs/node/pull/10109
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>

doc/api/tls.md

@@ -402,7 +402,7 @@ connections on the specified `port` and `hostname`.
 This function operates asynchronously. If the `callback` is given, it will be
 called when the server has started listening.
 
-See `net.Server` for more information.
+See [`net.Server`][] for more information.
 
 ### server.setTicketKeys(keys)
 <!-- YAML