[w3c/browser-payment-api] Editorial: event `.target` attribute should be relatedTarget (#513)

As per the DOM spec, I believe we need to talk about the relatedTarget of the event (as opposed to the value of the target attribute).   

Affects text in `updateWith()` and possibly other places where we perform target type checks. 

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/w3c/browser-payment-api/issues/513