Cookbook: mentions of Intl.DurationFormat

[o-t-w]

There are two mentions of Intl. DurationFormat in the Cookbook that can perhaps be updated?

"If you have Intl.DurationFormat, then you can do this with until.toLocaleString() and untilMonths.toLocaleString(). This example will be updated when that becomes possible."

"Note that this does not work unless you have Intl.DurationFormat, which is still an early-stage proposal."

Intl.DurationFormat is stage 4. It is implemented in Safari, Chrome/Edge and Firefox Nightly.