Bump redis from 2.8.0 to 3.1.1

Bumps [redis](https://github.com/NodeRedis/node-redis) from 2.8.0 to 3.1.1.
- [Release notes](https://github.com/NodeRedis/node-redis/releases)
- [Changelog](https://github.com/NodeRedis/node-redis/blob/master/CHANGELOG.md)
- [Commits](redis/node-redis@v.2.8.0...v3.1.1)

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

Author: dependabot[bot]