Rollup merge of #85974 - GuillaumeGomez:td-align, r=jsha

td align attribute

This is a follow-up of #85972. I have put this one on its own because it changes the display:

![Screenshot from 2021-06-03 21-49-11](https://user-images.githubusercontent.com/3050060/120703622-d533d280-c4b5-11eb-9519-ea1131a40bee.png)

Without align:

![Screenshot from 2021-06-03 21-49-15](https://user-images.githubusercontent.com/3050060/120703623-d5cc6900-c4b5-11eb-95f9-878d3915c7fb.png)

I also opened an issue about it: raphlinus/pulldown-cmark#533. However, I'm not sure if this is the right course of action... Should we instead ignore the warning?

r? ``@jsha``