Add comment / warning explaining inaccuracy of the next_expiry method in most cases.
Add comment / warning explaining inaccuracy of the next_expiry method in most cases.

likuolin/ib-ruby,ib-ruby/ib-ruby,likuolin/ib-ruby,malagant/ib-ruby,ib-ruby/ib-ruby,malagant/ib-ruby,malagant/ib-ruby,topofocus/ib-ruby,ib-ruby/ib-ruby,topofocus/ib-ruby,likuolin/ib-ruby,malagant/ib-ruby,topofocus/ib-ruby,ib-ruby/ib-ruby,likuolin/ib-ruby,topofocus/ib-ruby,malagant/ib-ruby,topofocus/ib-ruby,topofocus/ib-ruby,malagant/ib-ruby,topofocus/ib-ruby,malagant/ib-ruby,topofocus/ib-ruby,malagant/ib-ruby