fixes the following error message:
```
$ node-gyp rebuild
info This package requires node-gyp, which is not currently installed. Yarn will attempt to automatically install it. If this fails, you can run "yarn global add node-gyp" to manually install it.
[1/4] Resolving packages...
error Failed to auto-install node-gyp. Please run "yarn global add node-gyp" manually. Error: "Couldn't find any versions for \"node-gyp\" that matches \"latest\" in our cache (possible versions are \"\"). This is usually caused by a missing entry in the lockfile, running Yarn without the --offline flag may help fix this issue."
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
```
https://hydra.nixos.org/build/239684452
The main usecase for this variable is to append --production to yarn
which now got a whole lot easier because you no longer need to repeat
the defaults.