Add 6.6.2 to CHANGELOG

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

CHANGELOG

@@ -3,6 +3,9 @@ v 6.7.0
   - Add edit file button to MergeRequest diff
   - Public groups (Jason Hollingsworth)
+v 6.6.2
+  - Fix 500 error on branch/tag create or remove via UI
+
 v 6.6.1
   - Fix 500 error on files tab if submodules presents
@@ -655,4 +658,4 @@ v 0.8.0
   - stability
   - security fixes
   - increased test coverage
-  - email notification
\ No newline at end of file
+  - email notification