[Tests] up to `node` `v12.11`, `v11.15`, `v10.16`, `v9.11`, `v8.16`, `v6.17`, `v4.9`; use `nvm install-latest-npm`
[Tests] up to `node` `v12.11`, `v11.15`, `v10.16`, `v9.11`, `v8.16`, `v6.17`, `v4.9`; use `nvm install-latest-npm`

es-shims/Array.prototype.flatMap