Fix errata link text

[mattgarrish]

This code changes the errata links from "Errata exists" to the URL to the errata file.

Ideally, we'll be able to strip this code whenever speced/respec#4446 is resolved, but all the live notes currently say errata exists for them.

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[iherman]

Shouldn't the same changes be done on the three rec texts, too? We may republish new versions within 2-3 months to handle the obvious errata, and we shouldn't expect that respec issue to be handled with a high priority...

[mattgarrish]

Ya, good point. Probably over-optimistic on my part to think it'll be fixed quickly. I'll add to those, as well.