Update CHANGELOG

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CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
-v 8.2.0 (unreleased)
-  - Improved performance of replacing references in comments
-  - Fix duplicate repositories in GitHub import page (Stan Hu)
-  - Show last project commit to default branch on project home page
-  - Highlight comment based on anchor in URL
-  - Adds ability to remove the forked relationship from project settings screen. (Han Loong Liauw)
-  - Improved performance of sorting milestone issues
-  - Allow users to select the Files view as default project view (Cristian Bica)
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 v 8.1.0 (unreleased)
   - Ensure MySQL CI limits DB migrations occur after the fields have been created (Stan Hu)
   - Redirect to a default path if HTTP_REFERER is not set (Stan Hu)
   - Send an email to admin email when a user is reported for spam (Jonathan Rochkind)
   - Show notifications button when user is member of group rather than project (Grzegorz Bizon)
   - Fix bug preventing mentioned issued from being closed when MR is merged using fast-forward merge.
+  - Fix duplicate repositories in GitHub import page (Stan Hu)
   - Fix nonatomic database update potentially causing project star counts to go negative (Stan Hu)
   - Fix error preventing displaying of commit data for a directory with a leading dot (Stan Hu)
   - Speed up load times of issue detail pages by roughly 1.5x