title: Bokeh Multi line plots doesn't show
body: <p>I have a dataframe like below</p>
  
  <pre><code>    data_date  created_time  order_number
  0  2017-02-01         00:00           204
  1  2017-02-01         10:00            85
  2  2017-02-02         20:00            73
  3  2017-02-02         13:00            79
  4  2017-02-03         14:00           166
  </code></pre>
  
  <p>So what I want to do is to visualize the booking amount in hourly basis each day . The line plot will differ based on the data_date column, so there should be 3 lines on the graph.</p>
  
  <p>Here is the code I made with bokeh library</p>
  
  <pre><code>source = ColumnDataSource(hourly_booking)
  colormap = CategoricalColorMapper(factors=hourly_booking['data_date'].unique(), palette=['red', 'green', 'blue'])
  p = figure(x_axis_label = 'Time (24-Hour)', y_axis_label = 'Amount of order')
  p.multi_line(xs='created_booking', ys='order_number', source=source, line_color=dict(field='data_date', transform=colormap), line_width=5, line_alpha=0.6, legend='data_date')
  
  output_file('graph.html')
  show(p)
  </code></pre>
  
  <p>However the page goes blank so I don't know what went wrong with the codes.</p>
  
  <p><a href="https://i.stack.imgur.com/vQ0xi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vQ0xi.png" alt="enter image description here"></a></p>
  
  <p>What should I do?
  Any suggestion would be appreciated :)</p>