Broken placeholders in all examples

[jensenbox]

I fully recognize that the content is at the discretion of the end user of the templates however I am seeing that the templates are not currently rendering correctly from the website as the placehold.it service is now considered defunct and there are images referencing this now defunct service and therefore not rendering cleanly.

https://placehold.it/ is used for image placeholders, this service is now dead and has been replaced by https://placeholder.com

As validation, on this page https://get.foundation/emails/templates/basic.html you will see a broken image icon. This is because there is an image reference for https://placehold.it/200x50/663399 and if you were to visit that link you will see that the certificate is invalid.

Luckily, the replacement service at https://placeholder.com has an identical URL scheme and is functionally equivalent.

This problem can be remedied with a blanket search and replace.

https://placehold.it gets replaced with https://via.placeholder.com

Additionally, I recommend this operation be performed on all repositories in this organization.

If this is an acceptable solution, I would be happy to craft a few PRs that execute on this issue.