All images in example templates are broken

[viking1304]

Example templates use old HTTP links to plachold.it, which are now completely broken, for example http://placehold.it/200x50/663399

I replaced all of those links with new https://via.placeholder.com links and changed the display text (with text query parameter) to match the old images, since "Powered by HTML.COM" is very inconsistent. This text is not always visible and sometimes goes over the text with resolution.

Should I open a pull request with this change to this project or https://github.com/foundation/foundation-emails-template?

EDIT: Images are broken only if HTTP traffic is not allowed on your network (as in my corporate network). In cases where HTTP traffic is allowed, you will get the image.