Upgrade to Node 16

Created by: catrope

We had to revert a patch in Codex today because it pulled in an updated version of a library that uses a JS feature specific to Node 16. We didn't notice this at first because CI supports Node 16, but PatchDemo is still on Node 14.

It seems like it'd be relatively simple to upgrade to Node 14: change 14.x to 16.x here, and install the new package on the cloud instance that runs PatchDemo. I checked and the nodejs package in the 16.x PPA has the same dependencies as the one in the 14.x PPA, so this should be a smooth upgrade.

I'd be happy to take a stab at this myself, but I figured I'd file an issue first and wait a few days to see if anyone's going to tell me that it's not that simple.