title: Bokeh: DateRangeSlider decreases the year by 1 when the chosen start date is Jan 1st
body: <p>While I was trying out DateRangeSlider for another question here on SO, I found out that the start date 01/01/2017 was getting changed to 01/01/2016 on the slider. When I slid the date to Jan 2nd, it displayed the year correctly. It seems like a bug. If not, how do I fix it?</p>
  
  <p><a href="https://i.stack.imgur.com/ObzFI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ObzFI.png" alt="DateRangeSlider example"></a></p>
  
  <p>Below is the code that I used:</p>
  
  <pre><code>from datetime import date
  
  from bokeh.models.widgets import DateRangeSlider
  from bokeh.layouts import layout
  
  from bokeh.io import curdoc
  
  date_range_slider = DateRangeSlider(title="Date Range: ", start=date(2017, 1, 1), end=date.today(), value=(date(2017, 9, 7), date(2017, 10, 15)), step=1)
  
  l = layout(children=[[date_range_slider]], sizing_mode='fixed')
  curdoc().add_root(l)
  curdoc().title = "DateRangeSlider Example"
  </code></pre>