update CHANGELOG for release 3.0.0-rc.6 (#27)
update CHANGELOG for release 3.0.0-rc.6 (#27)

* update CHANGELOG for release 3.0.0-rc.6

* Add comma

Co-authored-by: John Lyons <ccdf991c5bb9582918d954f6f7ebf5e3ee6e9738@blackbaud.com>
blackbaud/skyux,blackbaud/skyux,blackbaud/skyux