Update CHANGELOG-EE.md for 10.5.3-ee

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CHANGELOG-EE.md

 Please view this file on the master branch, on stable branches it's out of date.
 
+## 10.5.3 (2018-03-01)
+
+### Security (2 changes)
+
+- Project can no longer be shared between groups when both member and group locks are active.
+- Prevent new push rules from using non-RE2 regexes.
+
+### Fixed (1 change)
+
+- Fix LDAP group sync no longer configurable for regular users.
+
+
 ## 10.5.2 (2018-02-25)
 
 - No changes.