title: Bokeh Error when making simple widget in Python
body: <p>I keep getting this ImportError for just trying to set up a basic widget slider. Below is the input and error message.</p>
  <pre><code>import bokeh
  from bokeh.io import output_notebook, show
  import bokeh.models.widgets
  from bokeh.models.widgets import Slider
  
  slider = Slider(start = 0, end = 10 , value = 1, step=.1, title = 'do nothing')
  
  show(slider)
  </code></pre>
  <pre><code>ImportError                               Traceback (most recent call last)
  &lt;ipython-input-100-2c4894dccaf0&gt; in &lt;module&gt;()
       10 slider = Slider(start = 0, end = 10 , value = 1, step=.1, title = 'do nothing')
       11 
  ---&gt; 12 show(slider)
  
  11 frames
  /usr/local/lib/python3.6/dist-packages/tornado/gen.py in &lt;module&gt;()
       79 import types
       80 
  ---&gt; 81 from tornado.concurrent import (
       82     Future,
       83     is_future,
  
  ImportError: cannot import name 'future_set_exc_info'
  
  ---------------------------------------------------------------------------
  NOTE: If your import is failing due to a missing package, you can
  manually install dependencies using either !pip or !apt.
  
  To view examples of installing some common dependencies, click the
  &quot;Open Examples&quot; button below.
  </code></pre>
  <p>I do have bokeh package installed as well. Not sure what the issue is. Any help is appreciated.</p>