fix typo in comment (go-sql-driver#1647)

Fix go-sql-driver#1646

Author: minhquang4334

AUTHORS

@@ -92,6 +92,7 @@ Paul Bonser <misterpib at gmail.com>
 Paulius Lozys <pauliuslozys at gmail.com>
 Peter Schultz <peter.schultz at classmarkets.com>
 Phil Porada <philporada at gmail.com>
+Minh Quang <minhquang4334 at gmail.com>
 Rebecca Chin <rchin at pivotal.io>
 Reed Allman <rdallman10 at gmail.com>
 Richard Wilkes <wilkes at me.com>

connection.go

@@ -435,7 +435,7 @@ func (mc *mysqlConn) getSystemVar(name string) ([]byte, error) {
 	return nil, err
 }
 
-// finish is called when the query has canceled.
+// cancel is called when the query has canceled.
 func (mc *mysqlConn) cancel(err error) {
 	mc.canceled.Set(err)
 	mc.cleanup()