Add *.squarecdn.com to the yellowlist

[GLips]

Checkout flows that rely on Square's JS library are getting blocked by Privacy Badger by default. I think this could be added to the yellowlist.

[ghostwords]

Hello and thanks for opening an issue!

I don't see squarecdn.com domains blocked in any pre-trained lists, but I do see it in some error reports (submitted via the "Report broken site" button).