Event.to_hash sometimes contains anonymous modules or classes, which cannot be dumped to YAML

It's common to have code like this:

``` ruby
SentryJob = Struct.new(:event) do
  def perform
    Raven.send_event(event)
  end
end

Raven.configure do |config|
  config.async = lambda { |event|
    Delayed::Job.enqueue SentryJob.new(event.to_hash)
  }
end
```

`event.to_hash` can contain an anonymous module, which cannot be dumped to YAML formats for use in a job processor.
