title: plotly express plot not shown in jupyter notebook
body: <p>I am using plotly express and just copied the official example from the below website in my jupyter notebook. The plot didn't show after running fig.show().</p>
  
  <p><a href="https://plot.ly/python/plotly-express/" rel="nofollow noreferrer">https://plot.ly/python/plotly-express/</a></p>
  
  <pre><code>import plotly.express as px
  df = px.data.iris()
  fig = px.scatter(df, x="sepal_width", y="sepal_length")
  fig.show()
  </code></pre>
  
  <p>I did install pip3 install dash==1.8.0</p>
  
  <p>I am using python 3.5</p>
  
  <p>Thanks for your help.</p>
  
  <p>Regards</p>
  
  <hr>
  
  <p>Update:</p>
  
  <p>I think i have to run it from .py file directly instead of using jupyter notebook. It works sometimes. Sometime, it doesn't work after opening a new browser. The error say:</p>
  
  <p>This site can’t be reached
  127.0.0.1 refused to connect.</p>
  
  <p>not sure what is the problem?</p>
  
  <p>anyone can help? Thanks</p>