Redis cleanSnapshots: wrong number of arguments for 'del' command

[TyGuy]

I am using the 'redis' store type with a non-zero maxSnapshotsCount option. When saving a snapshot, I get this error from redis client:

ReplyError: ERR wrong number of arguments for 'del' command
/app/node_modules/redis-parser/lib/parser.js in parseError at line 193:12

I've noticed this happens specifically when there are no snapshots that need to be cleaned (i.e. if the maxSnapshotCount was 5, but the number of snapshots is 1, (or anything less than 6 actually)). It seems like redis.del is getting called even when there are no items to call it on.

I'm on my way to fixing this, and will open a PR for it. But wanted to create this issue to document the bug.