Partial update behavior

I got issue with localized fields(mongoid), after migrating from `tire` gem.

```ruby
class Book
  include Mongoid::Document
  include Elasticsearch::Model
  include Elasticsearch::Model::Callbacks

  field :title, localized: true

  mapping do
    indexes :title, analyzer: "russian_morphology"
  end

  def as_indexed_json(opts={})
    {
      title: title
    }
  end
end

book = Book.create(title: "My book")
book.title = "My book 2"

book.changed_attributes # => {title: {ru: "My book 2"}}
book.as_indexed_json # => {title: "My book 2}

book.save
# Elasticsearch::Transport::Transport::Errors::BadRequest:
#       [400] {"error":"MapperParsingException[failed to parse [title]]; nested: ElasticsearchIllegalArgumentException[unknown property [ru]]; ","status":400}

```
Can we change this behavior a bit?