build: check against latest 12.x and 14.x

[michaelfig]

This change has dapp-encouragement tested against the latest Node.js in the 12.x and 14.x lineage.

Also, reenable Yarn and Go caches.

[warner]

Sounds good to me, although I'm a tiny bit nervous about allowing CI to float. Our docs will say "requires node 12.16.1 or higher", or something, but we'll only be testing against 12.18.52, or something. If one of us starts depending upon something in the latest 12.x, but the others (or downstream users) haven't updated their Node in a while, CI won't catch it.

OTOH, if something in the latest 12.x changes and stops working with our tree, this kind of CI would catch it, and would catch it more reliably than hoping one of us randomly upgrades and notices. So it's a bit of a double-edged sword. If cycles were free, we could test against both some fixed minimum (which would be what our docs would doc as our minimum supported Node), and the latest 12.x, and hope the whole range in between is basically covered by testing the two endpoints.

But testing both seems like overkill, and if we're only testing one, I'm ok with either.

[michaelfig]

If cycles were free, we could test against both some fixed minimum (which would be what our docs would doc as our minimum supported Node), and the latest 12.x, and hope the whole range in between is basically covered by testing the two endpoints.

Cycles virtually are free, because all the branches of a testing matrix are executed in parallel. So, I'll make that change.

But testing both seems like overkill, and if we're only testing one, I'm ok with either.

"Overkill" was my former middle name. 😉 Let's do both for the test-all-packages job, but leave the rest as 12.x, if that works for you.