traefik@1: fix build by downgrading node@16 to node@14

[cho-m]

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Another build failure due to node@16 (and probably node-sass) seen in #76791 (comment)

Unlike #77018, I didn't add a comment as traefik@1 is a versioned formula (traefik is v2 and doesn't have node dependency). If a comment is preferred, it can be added.

I confirmed build failure with original Formula on local system with --build-from-source.
Also confirmed successful build after downgrade to node@14:

🍺  /opt/homebrew/Cellar/node@14/14.16.1_1: 4,377 files, 59.6MB
==> Installing traefik@1
==> yarn upgrade
==> yarn install
==> yarn run build
==> go generate
==> go build -o /opt/homebrew/Cellar/traefik@1/1.7.30/bin/traefik ./cmd/traefik
==> Caveats
traefik@1 is keg-only, which means it was not symlinked into /opt/homebrew,
because this is an alternate version of another formula.

If you need to have traefik@1 first in your PATH, run:
  echo 'export PATH="/opt/homebrew/opt/traefik@1/bin:$PATH"' >> ~/.zshrc


To have launchd start traefik@1 now and restart at login:
  brew services start traefik@1
Or, if you don't want/need a background service you can just run:
  traefik
==> Summary
🍺  /opt/homebrew/Cellar/traefik@1/1.7.30: 7 files, 78.9MB, built in 2 minutes 6 seconds

[BrewTestBot]

🤖 A scheduled task has triggered a merge.