title: '__init__() got an unexpected keyword argument' error in Dash
body: <p>I am working on Jupyter Notebook and i am trying to use an external css sheet for a Dash app
  but i get the error above, Forgive me if it’s something very obvious as i am very new to this.</p>
  
  <pre><code>import dash
  import dash_core_components as dcc
  import dash_html_components as html
  from dash.dependencies import Input, Output
  from jupyter_plotly_dash import JupyterDash
  
  
  external_stylesheets = ["https://codepen.io/chriddyp/pen/bWLwgP.css"]
  
  app = JupyterDash(__name__, external_stylesheets=external_stylesheets)
  
  app.layout = html.Div([
      dcc.Input(id='my-id', value='initial value', type='text'),
      html.Div(id='my-div')
  ])
  
  
  @app.callback(
      Output(component_id='my-div', component_property='children'),
      [Input(component_id='my-id', component_property='value')]
  )
  def update_output_div(input_value):
      return 'You\'ve entered "{}"'.format(input_value)
  
  app
  
  Out: TypeError: __init__() got an unexpected keyword argument 'external_stylesheets'
  
  </code></pre>