Improve CHANGELOG entry

actionview/CHANGELOG.md

-* Deprecate `AbstractController::Base::parent_prefixes`. Override `AbstractController::Base::local_prefixes` when you want to change where to find views.
+*   Deprecate `AbstractController::Base.parent_prefixes`.
+    Override `AbstractController::Base.local_prefixes` when you want to change
+    where to find views.
 
     *Nick Sutterer*