Typo in the comment of mysqlConn.cancel(): 'finish' should be 'cancel'

[minhquang4334]

Issue description

There is a typo in the comment of mysqlConn.cancel()
https://github.com/go-sql-driver/mysql/blob/master/connection.go#L438

Example code

// finish is called when the query has canceled.
func (mc *mysqlConn) cancel(err error) {
	mc.canceled.Set(err)
	mc.cleanup()
}

Error log

If you have an error log, please paste it here.

Configuration

Driver version (or git SHA): 1.8.1

Go version: run go version in your console

Server version: E.g. MySQL 5.6, MariaDB 10.0.20

Server OS: E.g. Debian 8.1 (Jessie), Windows 10