doc: update CHANGELOG.md

Author: flavorjones

CHANGELOG.md

@@ -4,6 +4,17 @@ Nokogiri follows [Semantic Versioning](https://semver.org/), please see the [REA
 
 ---
 
+## 1.13.9 / unreleased
+
+### Security
+
+* [CRuby] Vendored libxml2 is updated to address [CVE-2022-2309](https://nvd.nist.gov/vuln/detail/CVE-2022-2309), [CVE-2022-40304](https://nvd.nist.gov/vuln/detail/CVE-2022-40304), and [CVE-2022-40303](https://nvd.nist.gov/vuln/detail/CVE-2022-40303). See [GHSA-2qc6-mcvw-92cw](https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-2qc6-mcvw-92cw) for more information.
+
+### Dependencies
+
+* [CRuby] Vendored libxml2 is updated to [v2.10.3](https://gitlab.gnome.org/GNOME/libxml2/-/releases/v2.10.3) from v2.9.14.
+* [CRuby] Vendored libxslt is updated to [v1.1.37](https://gitlab.gnome.org/GNOME/libxslt/-/releases/v1.1.37) from v1.1.35.
+
 ## 1.13.8 / 2022-07-23
 
 ### Deprecated