update changelog

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 7.13.0
-v 7.14.0 (unreleased)
   - Remove repository graph log to fix slow cache updates after push event (Stan Hu)
-  - Fix label read access for unauthenticated users (Daniel Gerhardt)
-  - Fix OAuth provider bug where GitLab would not go return to the redirect_uri after sign-in (Stan Hu)
-  - Fix file upload dialog for comment editing (Daniel Gerhardt)
-  - Expire Rails cache entries after two weeks to prevent endless Redis growth
-  - Add support for destroying project milestones (Stan Hu)
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-v 7.13.0 (unreleased)
   - Only enable HSTS header for HTTPS and port 443 (Stan Hu)
   - Fix user autocomplete for unauthenticated users accessing public projects (Stan Hu)
   - Fix redirection to home page URL for unauthorized users (Daniel Gerhardt)