title: Axis label font styles not changing bokeh
body: <p>I have a figure <code>p</code>, </p>
  
  <pre class="lang-py prettyprint-override"><code>p = bokeh.plotting.figure(
      width=300,
      height=250,
      x_axis_label='this is the x axis',
      y_axis_label="this is the y axis',
  )
  </code></pre>
  
  <p>By default, the x and y axis label is in italic font style. I would like to change it to the normal style. </p>
  
  <p>However, when I do: </p>
  
  <pre class="lang-py prettyprint-override"><code>p.yaxis.axis_label_text_font_style = 'normal'
  </code></pre>
  
  <p>The y axis font style remains italic, and I get no error message. </p>
  
  <p>What am I missing here? </p>
  
  <p>I have also tried </p>
  
  <pre class="lang-py prettyprint-override"><code>p.axis.axis_label_text_font_style = 'normal'
  </code></pre>
  
  <p>not specifying the axis, and  still there was no change. </p>