docs: bump hextra to v0.4.0

[imfing]

What does this change

Bumping the version of the docs theme version, and fixes small styling issues, including the order of the blog posts.

What issue does it fix

Bumping the version of the theme which fixes several issues including the order of the blog posts

Details

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Checklist

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• Did you write documentation?
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Reviewer Checklist

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[schristoff]

ty so much, we noticed yesterday the problem with blog posts and just released an import one today :) this is much appreciated

[imfing]

@schristoff apologies for the inconvenience as i didn't notice the order issue of the blog section until a few days ago.

thanks again for adopting https://github.com/imfing/hextra/
feel free to send issues for any bugs or feature requests, i would be happy to help with improving Porter's docs