Update databases/redis to 4.0.4.

Upgrade urgency CRITICAL: Several PSYNC2 bugs can corrupt the slave
data set after a restart and a successful PSYNC2 handshake.

- Fix the "PSYNC after restart" problem.
- LFU fixes improve the ability of Redis to correctly estimate the
  popularity of keys.
- Security fix related to loading a corrupted Cluster state from a
  corrupted file.
- Other bugfixes.

(fhajny)