Homepage last modified date 0001-01-01

[LilithHafner]

Describe the bug
The homepage shows "Last modified: 0001-01-01. This site is powered by Netlify, Franklin.jl..."

Other pages are fine.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'https://julialang.org/
2. Scroll down to footer
3. See error

[ViralBShah]

Perhaps relevant? tlienart/Franklin.jl#700

[LilithHafner]

I don't think the solution in that issue fixes this because other pages which use the same Last modified: {{ fill fd_mtime }}. invocation are fine. I'm guessing it has to do with special handling we give the homepage for faster load time.

[IanButterworth]

I think we just need to edit the homepage?

[IanButterworth]

I edited index.html in #2157 but the home page date is still bad on the preview and now deployed version.

@tlienart any idea?