Fix Python version badge
<tr>
<td>Latest Release</td>
<td>
- <img src="https://badge.fury.io/gh/bokeh%2Fbokeh.svg" alt="Latest release version" />
- <a href="https://badge.fury.io/js/%40bokeh%2Fbokehjs">
+ <img src="https://badge.fury.io/py/bokeh.svg" alt="pypi version" />
<img src="https://badge.fury.io/js/%40bokeh%2Fbokehjs.svg" alt="npm version">
</a>
</td>
