title: Rails 5 ancestry gem: Update parent_id with ajax return nil
body: <p>I try to update parent_id in ancestry gem but return nil.Send parent_id with ajax to update action but save nil.Categories system works like, click input to change parent_id then open modal, selected a category, close modal then save category as changed.But when click to update save nil. How can I fix it ?</p>
  
  <p>ajax code</p>
  
  <pre><code>  $.ajax
      type: 'GET'
      data: {parent_id: this.id}
  </code></pre>
  
  <p>categories_controller.rb</p>
  
  <pre><code>def update
      @category.parent_id = params[:parent_id]
      @category.update_attributes(category_params)
    end
  </code></pre>
  
  <p>_category.haml</p>
  
  <pre><code>       %input.radio_category{:id =&gt; "#{category.id}", :name =&gt; "radio", :type =&gt; "radio", :value =&gt; "#{category.name}", remote: true, 'data-parent-id': category.id}&gt;
            = category.name
            - if category.has_children?
              = render partial: "category", locals: { collection: category.children }
  </code></pre>
  
  <p>Thanks in advance!</p>