New image placeholders

[seho-nl]

The images in the current documentation links to an image placeholder endpoint that does not exists anymore. It looks like the team behind https://placehold.it either quit or moved it to https://placehold.co.

Either way, I updated the documentation files so that the images render properly again.

[joeworkman]

Closing in favor of #2106 which was merged. Thanks for the contribution!

[seho-nl]

I don't really understand why you choose #2106 over this merge.
#2016 fixes only one page where my merge looked at all other pages as well.

[joeworkman]

Thanks for the feedback guys. I will get this fixed this afternoon.

[joeworkman]

Shipping this as 2.5.1 now. Thanks guys!

[simonschaufi]

@joeworkman I still don't see the new placeholder images on the website. Is it deployed already?

https://get.foundation/emails/docs/grid.html#offsets

[joeworkman]

All working. The site build was not working. Should be good now.

Go check out Inky 2! This basically consolidates Foundation for Email and Inky into one tool. It also has a ton more features now. The CLI version is the most tested and pretty stable (for me at least). I would love your feedback. https://github.com/foundation/inky/tree/feature/2.0-rust