Update changelog.md

Fixed typo
Merge pull request #445 from existentialism/patch-1

Fixed minor type in changelog.md
update the docs to reflect that Marionette.EventAggregator no longer wraps Backbone.Wreqr.EventAggregator (commit b51e1e3aa92dbc43a7423b3e29562d9a6f2f336a)
Merge pull request #446 from drewda/master

update the docs to reflect that Marionette.EventAggregator no longer wraps Backbone.Wreqr.EventAggregator