Load all of ActiveSupport

ActiveSupport has weird load order problems when loading only the
core extensions now.

For instance, active_support/core_ext/numeric/conversions.rb now
loads active_support/number_helper which needs
ActiveSupport::Autoload but doesn't require it, so causes a missing
constant error in MailCatcher.

Also tightening up the version constraint because I can't guarantee
backward compatibility now.
bundle update