title: Poison : unable to encode value
body: <p>I am not able to encode values which I am getting from Ecto query result  Poison encode method</p>
  
  <p><strong>Controller code:</strong></p>
  
  <pre><code>def companies(conn, params) do
      companies = Repo.all(
        from(
          c in Company,
          select: {c.name, c.uid},
          limit: 20
        )
      ) 
  
      conn
      |&gt; put_resp_header("content-type", "application/json; charset=utf-8")
      |&gt; send_resp(200, Poison.encode!(companies, pretty: true))
  end
  </code></pre>
  
  <p><strong>Template code :</strong> </p>
  
  <pre><code>&lt;div class="form-group row"&gt;
    &lt;%= label f, :company_id, class: "control-label" %&gt;
    &lt;%= select f, :company_id, @companies, class: "form-control"%&gt;
  &lt;%= error_tag f, :company_id %&gt;
  </code></pre>
  
  <p></p>
  
  <p><strong>Error message:</strong> </p>
  
  <pre><code>Request: GET /companies
  ** (exit) an exception was raised:
      ** (Poison.EncodeError) unable to encode value: {"Loews Corporation", 1000285930}
          (poison) lib/poison/encoder.ex:383: Poison.Encoder.Any.encode/2
          (poison) lib/poison/encoder.ex:268: anonymous fn/4 in Poison.Encoder.List.encode/3
          (poison) lib/poison/encoder.ex:269: Poison.Encoder.List."-encode/3-lists^foldr/2-0-"/3
          (poison) lib/poison/encoder.ex:269: Poison.Encoder.List.encode/3
          (poison) lib/poison.ex:41: Poison.encode!/2
  </code></pre>