revert conda badge update (not monthly value)
<td>Conda</td>
<td>
<a href="https://docs.bokeh.org/en/latest/docs/installation.html">
- <img src="https://img.shields.io/conda/dn/conda-forge/bokeh"
+ <img src="https://pyviz.org/_static/cache/bokeh_conda_downloads_badge.svg"
alt="Conda downloads per month" />
</a>
</td>
