title: Dynamically update the title in Dash Plotly
body: <p>I have created this very simplified example in which I would like to dynamically update the title of a chart as a dropdown label changes.
  Here's the code:</p>
  <pre><code>data = {'Stock': ['F',  'NFLX',  'AMZN'], 'Number': [10, 15, 7]}
  df = pd.DataFrame(data, columns=['Stock', 'Number'])
  stock_options = df['Stock']
  
  app = dash.Dash(__name__)
  
  app.layout = html.Div(children=[
      html.H1(children='Example Bar Chart'),
      html.Div([
          dcc.Dropdown(
              id='dropdown',
              options=[{'label': i, 'value': i} for i in stock_options],
              value='F',
  
           ),
          html.Div(dcc.Graph(id='graph')),
      ]),
  ])
  
  
  @app.callback(
     Output(component_id='graph', component_property='figure'),
     Input(component_id='dropdown', component_property='value')
  )
  def update_graph(stock):
      msk = df.Stock.isin([stock])
      figure = px.bar(df[msk], x='Stock', y='Number', title=f&quot;{stock} open price&quot;)
  
      return figure
  
  
  if __name__ == '__main__':
      app.run_server(debug=True)
  </code></pre>
  <p>So, while keeping the same label in dropdown instead of 'F open price' in the title I would like to get 'Facebook open price'... and so on.
  I've tried to solve this with <code>map</code> but I couldn't get it working. Can someone point me in the direction on how to resolve this?
  Thanks in advance.</p>