Does not play well with "sphinx-last-updated-by-git" extension

Hi,

Not sure why but sphinx-multiversion does not work well with:
https://github.com/mgeier/sphinx-last-updated-by-git/
If I `make html` the plugin above works, but if I build with `sphinx-multiversion` it does not.

Would it be possible to either make it play ball or implement something that fills in `last_updated` in a similar fashion?
