[fetch] Clarify what origin the Request constructor needs to check the referrer URL against (#224)

Step 13.6 of https://fetch.spec.whatwg.org/#dom-request refers to `origin`, but that is not a variable defined before in this algorithm.  I think the intention is to say `entry settings object's origin` instead...

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/224