Poor rendering of pandas dataframes in the docs

[drbenvincent]

I just noticed that the rendering of dataframes are bad in the docs. By way of example from https://bambinos.github.io/formulae/notebooks/getting_started.html#Creating-and-accessing-design-matrices

This is what it looks like in Chrome:

And this is what is looks like in Safari:

I realise the issue is not emanating from this repo, and is likely a pandas or Jupyter or sphinx issue, but I thought I'd raise this in case nobody was aware.