title: Plotly: How to add volume to a candlestick chart
body: <p>code:</p>
  <pre><code>from plotly.offline import init_notebook_mode, iplot, iplot_mpl
      
  def plot_train_test(train, test, date_split):
      data = [Candlestick(x=train.index, open=train['open'], high=train['high'], low=train['low'], close=train['close'],name='train'),
             Candlestick(x=test.index, open=test['open'], high=test['high'], low=test['low'], close=test['close'],name='test')
              ]
              layout = {
                  'shapes': [
                      {'x0': date_split, 'x1': date_split, 'y0': 0, 'y1': 1, 'xref': 'x', 'yref': 'paper',
                       'line': {'color': 'rgb(0,0,0)', 'width': 1}}],
                  'annotations': [{'x': date_split, 'y': 1.0, 'xref': 'x', 'yref': 'paper', 'showarrow': False, 'xanchor': 'left','text': ' test data'},
                      {'x': date_split, 'y': 1.0, 'xref': 'x', 'yref': 'paper', 'showarrow': False, 'xanchor': 'right', 'text': 'train data '}] }
              figure = Figure(data=data, layout=layout)
              iplot(figure)
  </code></pre>
  <p>The above code is ok.But now I want to 'volume' in this candlestick chart</p>
  <p>code:</p>
  <pre><code>from plotly.offline import init_notebook_mode, iplot, iplot_mpl
          
  def plot_train_test(train, test, date_split):
      data = [Candlestick(x=train.index, open=train['open'], high=train['high'], low=train['low'], close=train['close'],volume=train['volume'],name='train'),
             Candlestick(x=test.index, open=test['open'], high=test['high'], low=test['low'],close=test['close'],volume=test['volume'],name='test')]
              layout = {
                  'shapes': [
                      {'x0': date_split, 'x1': date_split, 'y0': 0, 'y1': 1, 'xref': 'x', 'yref': 'paper',
                       'line': {'color': 'rgb(0,0,0)', 'width': 1}}
                  ],
                  'annotations': [
                      {'x': date_split, 'y': 1.0, 'xref': 'x', 'yref': 'paper', 'showarrow': False, 'xanchor': 'left',
                       'text': ' test data'},
                      {'x': date_split, 'y': 1.0, 'xref': 'x', 'yref': 'paper', 'showarrow': False, 'xanchor': 'right',
                       'text': 'train data '}
                  ]
              }
              figure = Figure(data=data, layout=layout)
              iplot(figure) 
  </code></pre>
  <p>error:</p>
  <blockquote>
  <p>ValueError: Invalid property specified for object of type
  plotly.graph_objs.Candlestick: 'volume'</p>
  </blockquote>