Bump npm from 6.4.1 to 6.14.6

Bumps [npm](https://github.com/npm/cli) from 6.4.1 to 6.14.6.
- [Release notes](https://github.com/npm/cli/releases)
- [Changelog](https://github.com/npm/cli/blob/latest/CHANGELOG.md)
- [Commits](npm/cli@v6.4.1...v6.14.6)

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

Author: dependabot[bot]