No testdata at current.

五步更新：

1. rm -rf ~/.nvm
2. . <(curl https://hydro.ac/nix.sh)
3. nix-env -iA nixpkgs.nodejs nixpkgs.yarn
4. nix-env -e hydro.sandbox && nix-env -iA nixpkgs.go-judge && ln -sf $(which go-judge) /usr/bin/hydro-sandbox
5. pm2 restart hydro-sandbox --update-env