Update custom-tls-logging.rst

[espritlibre]

fix: typo error in customformat example

Make sure these boxes are signed before submitting your Pull Request -- thank you.

• [ X] I have read the contributing guide lines at https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Contributing
• [ X] I have signed the Open Information Security Foundation contribution agreement at https://suricata-ids.org/about/contribution-agreement/
• [ ]X I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)

Link to redmine ticket:

Describe changes:

• fix typo error in documentation

PRScript output (if applicable):

[victorjulien]

I've taken this and another typo fix and merged it into a single commit which I merged in #4123. Thanks for the fix.