title: Deserialize Date in Marshmallow
body: <p>I have a Table (START_DATE , TEXT ,DECIMAL , INTEGER).
  I read the data from the DB and try to de serialize the data.</p>
  <pre><code>
  class Response(Schema):
      class Meta:
          json_module = simplejson
      data = fields.List(fields.List(fields.Raw()))
  
  </code></pre>
  <p>Response:</p>
  <pre><code>
  &quot;data&quot;: [
          [
              &quot;Tue, 26 Jan 2021 00:00:00 GMT&quot;,
              &quot;USD&quot;,
              78790.400000,
              79262
          ],
          [
              &quot;Mon, 25 Jan 2021 00:00:00 GMT&quot;,
              &quot;USD&quot;,
              68852.340000,
              77365
          ]
  
  </code></pre>
  <p>How can I change the dateformat to '%Y-%m-%dT%H:%M:%S%z'
  I did the below change but no change in the date format.</p>
  <pre><code>
  class Response(Schema):
      class Meta:
          json_module = simplejson
          dateformat = '%Y-%m-%dT%H:%M:%S%z'
      data = fields.List(fields.List(fields.Raw()))
  
  </code></pre>