title: Change in date from string to datetime object when converting pandas dataframe to dictionary
body: <p>I have the foll. dataframe:</p>
  
  <pre><code>                avi       fi_id       dates
  2017-07-17  0.318844    zab_a_002  2017-07-17
  </code></pre>
  
  <p>When I convert it into a dictionary, I get this:</p>
  
  <pre><code>dict_avi = df.reset_index().to_dict('records')
  
  [{'index': Timestamp('2017-07-17 00:00:00'), 'avi': 0.3188438263036763, 'fi_id': 'zab_a_002', 'dates': datetime.date(2017, 7, 17)}]
  </code></pre>
  
  <p>Why did the dates column become a datetime object? How can I retain it as a string?</p>
  
  <p>Here are the dtypes:</p>
  
  <pre><code>avi        float64
  fi_id     object
  dates        object
  dtype: object
  </code></pre>