fix(docs): Set Permalink URL to AuthenticationSession struct (#2046)

* fix(oathkeeper): Set Permalink URL to AuthenticationSession struct

Use permalink to cater for changes to the code base.

* fix(docs): set correct line-break

* chore: point to master

---------

Co-authored-by: vinckr <[email protected]>

Author: muya

Diff for: docs/oathkeeper/pipeline/mutator.md

@@ -411,7 +411,7 @@ For more details please check [Session variables](../pipeline.md#session)
 This mutator allows for fetching additional data from external APIs, which can be then used by other mutators. It works by making
 an upstream HTTP call to an API specified in the **Per-Rule Configuration** section below. The request is a POST request and it
 contains JSON representation of
-[AuthenticationSession](https://github.com/ory/oathkeeper/blob/master/pipeline/authn/authenticator.go#L39) struct in body, which
+[AuthenticationSession](https://github.com/ory/oathkeeper/blob/master/pipeline/authn/authenticator.go#L45) struct in body, which
 is:
 
 ```json