Bump semver from 6.3.0 to 6.3.1 in /nextjs-demo

Bumps [semver](https://github.com/npm/node-semver) from 6.3.0 to 6.3.1.
- [Release notes](https://github.com/npm/node-semver/releases)
- [Changelog](https://github.com/npm/node-semver/blob/v6.3.1/CHANGELOG.md)
- [Commits](npm/node-semver@v6.3.0...v6.3.1)

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

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

Author: dependabot[bot]