Minor fix for the redis.Strings helper function.  Now properly parses a pipelined reply as a slice of strings.

Please see my Issue which talks about this problem.  I am simply trying to get a slice of strings back from the redis.Strings helper function from a pipelined call that contains a bunch of SET calls to Redis.  Redis returns OK as a result for all the matching SET calls, however I believe this is a legitimate bug where the redis.Strings function will return an empty slice instead of a proper slice that contains all that OK strings within it.