Bump semver from 5.4.1 to 5.6.0

Bumps [semver](https://github.com/npm/node-semver) from 5.4.1 to 5.6.0.
- [Release notes](https://github.com/npm/node-semver/releases)
- [Changelog](https://github.com/npm/node-semver/blob/master/CHANGELOG.md)
- [Commits](npm/node-semver@v5.4.1...v5.6.0)

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

Author: dependabot-support