html: update URL in comment

The comment contained a link that had a file name and ID that no longer existed, so change to the URL of the corresponding part of the latest page.

Change-Id: I74e0885aabf470facc39b84035f7a83fef9c6a8e
GitHub-Last-Rev: 5681c84d9f1029449da6860c65a1d9a128296e85
GitHub-Pull-Request: golang/go#36514
Reviewed-on: https://go-review.googlesource.com/c/go/+/214181
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/html/escape.go

@@ -12,7 +12,7 @@ import (
 
 // These replacements permit compatibility with old numeric entities that
 // assumed Windows-1252 encoding.
-// http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#consume-a-character-reference
+// https://html.spec.whatwg.org/multipage/parsing.html#numeric-character-reference-end-state
 var replacementTable = [...]rune{
 	'\u20AC', // First entry is what 0x80 should be replaced with.
 	'\u0081',