Update suricata-yaml.rst

[Momooou]

Added a missing full stop.

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• [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.io/about/contribution-agreement/
• [x] I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)

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Describe changes:

#suricata-verify-pr: #suricata-verify-repo: #suricata-verify-branch: #suricata-update-pr: #suricata-update-repo: #suricata-update-branch: #libhtp-pr: #libhtp-repo: #libhtp-branch: