Update CHANGELOG-EE.md for 12.9.1-ee

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CHANGELOG-EE.md

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+## 12.9.1 (2020-03-26)
+
+### Security (1 change)
+
+- Add NPM package versions SemVer validation.
+
+
 ## 12.9.0 (2020-03-22)
 
 ### Removed (1 change)

ee/changelogs/unreleased/security-path-traversal-npm-package-registry.yml

----
-title: Add NPM package versions SemVer validation
-merge_request:
-author:
-type: security