Update db_test.go

Author: kyleconroy

examples/booktest/sqlite/db_test.go

@@ -18,7 +18,7 @@ const (
 
 func TestBooks(t *testing.T) {
 	db, cleanup := sqltest.SQLite(t, []string{"schema.sql"})
-	defer sdb.Close()
+	defer db.Close()
 	defer cleanup()
 
 	ctx := context.Background()