refactor: modify the form of variable declarations

[CocaineCong]

I've changed the form of variable declarations which make the code look better (maybe...)

the comparison is following :

before:

var host = flag.String("host", "127.0.0.1", "MySQL host")
var port = flag.Int("port", 3306, "MySQL port")
var user = flag.String("user", "root", "MySQL user, must have replication privilege")
var password = flag.String("password", "", "MySQL password")

after:

var (
	host     = flag.String("host", "127.0.0.1", "MySQL host")
	port     = flag.Int("port", 3306, "MySQL port")
	user     = flag.String("user", "root", "MySQL user, must have replication privilege")
	password = flag.String("password", "", "MySQL password")
)

I am not sure if this change is necessary, but if not, please ignore. :)
thank u for reviewing. 🫡