Updates the EndDatePropagator to add error messages to the propagated object at a lower level.
# Behavior in 1.2.0
obj = EndDatePropagator.call(something)
obj.errors.details
# => [ base: { message: 'Some Error Message' } ]
# Behavior in 1.2.1
obj = EndDatePropagator.call(something)
obj.errors.details
# => [ base: 'Some Error Message' ]This is compatible with the default error flash message used in the responders gem. In v 1.2.0, the flash message would render the hash, not just the value associated with :message.