Update CHANGELOG.md for 10.6.6

[ci skip]

CHANGELOG.md

@@ -457,6 +457,16 @@ entry.
 - Upgrade Gitaly to upgrade its charlock_holmes.
+## 10.6.6 (2018-05-28)
+
+### Security (4 changes)
+
+- Do not allow non-members to create MRs via forked projects when MRs are private.
+- Prevent user passwords from being changed without providing the previous password.
+- Fix API to remove deploy key from project instead of deleting it entirely.
+- Fixed bug that allowed importing arbitrary project attributes.
+
+
 ## 10.6.5 (2018-04-24)
 ### Security (1 change)