Fix sidekiq log link

Use relative link rather than URL

doc/user/project/integrations/slack.md

@@ -28,7 +28,7 @@ Your Slack team will now start receiving GitLab event notifications as configure
 ## Troubleshooting
 
 If you're having trouble with the Slack integration not working, then start by
-searching through the [Sidekiq logs](https://docs.gitlab.com/ee/administration/logs.html#sidekiqlog)
+searching through the [Sidekiq logs](/doc/administration/logs.md#sidekiqlog)
 for errors relating to your Slack service.
 
 ### Something went wrong on our end