Bump tar from 2.2.1 to 2.2.2 in /docs/reveal.js-3.8.0

Bumps [tar](https://github.com/npm/node-tar) from 2.2.1 to 2.2.2.
- [Release notes](https://github.com/npm/node-tar/releases)
- [Commits](isaacs/node-tar@v2.2.1...v2.2.2)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]