build(deps): [security] bump npm from 6.4.1 to 6.13.4 (#287)

Bumps [npm](https://github.com/npm/cli) from 6.4.1 to 6.13.4. **This update includes security fixes.**
- [Release notes](https://github.com/npm/cli/releases)
- [Changelog](https://github.com/npm/cli/blob/latest/CHANGELOG.md)
- [Commits](npm/cli@v6.4.1...v6.13.4)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>