Bump semver from 5.7.1 to 5.7.2 in /docs (#284)

Bumps [semver](https://github.com/npm/node-semver) from 5.7.1 to 5.7.2.
- [Release notes](https://github.com/npm/node-semver/releases)
- [Changelog](https://github.com/npm/node-semver/blob/v5.7.2/CHANGELOG.md)
- [Commits](npm/node-semver@v5.7.1...v5.7.2)

---
updated-dependencies:
- dependency-name: semver
  dependency-type: indirect
...

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