Plugins using rails-observers

If you have a plugin that uses rails-observers (e.g. implementing
ActionController::Caching::Sweeper or ActiveRecord::Observer), please be
aware that the dependency has been removed in Foreman core in ticket #14434.

Any plugin using it should add an explicit dependency on the gem. It
will remain packaged and probably installed for the foreseeable future
as it's used by audited.

··· -- Dominic Cleal