BITCOUNT not support bit option

[kay011]

From version 7.0.0, Redis added the BYTE|BIT option for BITCOUNT.

For example:

127.0.0.1:6379> setbit mykey 7 1
(integer) 0
127.0.0.1:6379> setbit mykey 6 1
(integer) 0
127.0.0.1:6379> bitcount mykey 6 7 
(integer) 0
127.0.0.1:6379> bitcount mykey 6 7 bit
(integer) 2
127.0.0.1:6379> bitcount mykey 6 7 byte
(integer) 0

But go-redis does't support this option in lastest version.

[tzq0301]

Can be closed by #2887