image not respecting alignement with png in .rst

I decided to open a follow-up of [this thread](https://github.com/github/markup/issues/163) as the bug seems to be fixed but fails on some more specific image type.

I try to align the content of my readme.rst file to use as a long description in my pypi release. using the `.. raw::` directive is then impossible.

A common way to do it (that works on both sphinx and pypi) is:

```rst
.. image:: toto.png
:align: center
```

It seems this is not taken into account when generating .png preview as shown in this [gist](https://gist.github.com/jmi2k/f422df7d4a67dde9c19e74d091c3582e) where the .svg is correctly aligned and the .png is not.