Add public groups to change log

CHANGELOG

 v 6.7.0
   - Add support for Gemnasium as a Project Service
   - Add edit file button to MergeRequest diff
+  - Public groups (Jason Hollingsworth)
 
 v 6.6.1
   - Fix 500 error on files tab if submodules presents
@@ -654,4 +655,4 @@ v 0.8.0
   - stability
   - security fixes
   - increased test coverage
-  - email notification
+  - email notification
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