Update databases/redis to 4.0.2.

Significant bugs fixed:

1. A number of bugs were fixed in the area of PSYNC2 replication in
thecspecific area of restarting an instance with an RDB file having
the repliacation meta-data to continue without a full
resynchronization.

2. AOF flush on SHUTDOWN did not cared to really write the AOF buffers
(not in the kernel but in the Redis process memory) to disk before
exiting. Calling SHUTDOWN during traffic resulted into not every
operation to be persisted on disk.

3. The SLOWLOG could reference values inside string objects stored at
keys, creating a race condition during FLUSHALL ASYNC while the DB is
reclaimed in another thread.

(fhajny)