Update the redis version in the Redis-mock

[sozakir]

Recently redis has fixed a vulnerability https://github.com/NodeRedis/node-redis/security/advisories/GHSA-35q2-47q7-3pc3, in the latest 3.1.2.

https://github.com/NodeRedis/node-redis/pull/1595/files

I have created a PR for this #188. Plz review @kamiljano