Fix API docs formatting

[svekars]

Fix #178
Test plan:

• Checkout this PR
• Run the grunt build locally as described in the README: https://github.com/pytorch/pytorch_sphinx_theme#local-development
• Open the api.html page to view the formatting which should look like this:

[NicolasHug]

Thanks a lot for fixing this @svekars .

I have checked out this PR locally and built the torchvision docs with it. I can confirm the docs look much better and I'm not observing any regression on the rest of the docs.

FWIW, here's a before and after renderring of the torchvision docs. They look much better with this PR.

Currently on main:

With this PR:

[svekars]

Thanks so much for verifying @NicolasHug !