title: render json serializer not returning json
body: <p>In our API, we are using ActiveModel Serializer to return json.</p>
  
  <pre><code>render json: { taxon: TaxonSerializer.new(taxon) }
  </code></pre>
  
  <p>What I'm getting back is </p>
  
  <pre><code>{
      "taxon": "#&lt;TaxonSerializer:0x007ff704b6a820&gt;"
  }
  </code></pre>
  
  <p>What I'm expecting is </p>
  
  <pre><code>"taxon": {
      "name": "Test",
      "handle": "test"
  }
  </code></pre>
  
  <p>Does anyone know what's wrong? Maybe we aren't using the right version of ActiveModel Serializer?</p>
  
  <p>This used to work but now, it doesn't work anymore.</p>