fix new-lined query execution in master DB node.

# Issue
Such a following query is executed in master DB node with EngineGroup.

```go
s := engineGroup.NewSession(); // create session from EngineGroup.

sql := `
SELECT * FROM USER;
`;

type User struct { ... };
var users []User;
err := s.Sql(sql).Find(&users); // executed to master DB node.

```

session_raw.go

@@ -33,7 +33,7 @@ func (session *Session) queryRows(sqlStr string, args ...interface{}) (*core.Row
 
 	if session.isAutoCommit {
 		var db *core.DB
-		if session.sessionType == groupSession && strings.EqualFold(sqlStr[:6], "select") {
+		if session.sessionType == groupSession && strings.EqualFold(strings.TrimSpace(sqlStr)[:6], "select") {
 			db = session.engine.engineGroup.Slave().DB()
 		} else {
 			db = session.DB()