Fix invalid resposne of COMMAND

[zsh1995]

When I use github.com/go-redis/redis/v8 redis.Command would return a error:

redis: can't parse array reply: "$9440"

The reason is that WriteBulk append $len(str) in front of the data. Correct response of Command should be $len(commands).

[alicebob]

The reason is that `WriteBulk` append `$len(str)` in front of the data. Correct response of `Command` should be `$len(commands)`.

Thanks for the PR! I'll have a (better) look soon.

[alicebob]

Thanks! Good catch.