database/sql: fix comment grammar

Change-Id: I92d8c93967c5ec57f07151affd0041f00e405057
GitHub-Last-Rev: 2dea977d938a504604aed6a9ae87986001f96acd
GitHub-Pull-Request: golang/go#30551
Reviewed-on: https://go-review.googlesource.com/c/go/+/164970Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/database/sql/driver/driver.go

@@ -26,7 +26,7 @@ import (
 //   time.Time
 //
 // If the driver supports cursors, a returned Value may also implement the Rows interface
-// in this package. This is used when, for example, when a user selects a cursor
+// in this package. This is used, for example, when a user selects a cursor
 // such as "select cursor(select * from my_table) from dual". If the Rows
 // from the select is closed, the cursor Rows will also be closed.
 type Value interface{}