Add Changelog entry for upload link in snippet fix

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.8.0 (unreleased)
+  - Fix error when using link to uploads in global snippets
   - Assign labels and milestone to target project when moving issue. !3934 (Long Nguyen)
   - Project#open_branches has been cleaned up and no longer loads entire records into memory.
   - Escape HTML in commit titles in system note messages