"Fix" twitter badge broken by twitter API shutdown
<td>
<a href="https://twitter.com/bokeh">
- <img src="https://img.shields.io/twitter/follow/bokeh?color=blue&logo=twitter&style=for-the-badge"
+ <img src="https://img.shields.io/badge/follow-%40bokeh-blue?logo=twitter&style=for-the-badge"
alt="Follow Bokeh on Twitter" />
</a>
</td>
