add support for lastInsertId method on OCI8 Driver

public function lastInsertId($name = null)
{
    //TODO: throw exception or support sequences?
}

public function lastInsertId($name = null)
 {
        // For sequence
        if (is_string($name)) {
            // We can check eventually check the presence of the sequence in the table
            // USER_SEQUENCES
            $sql = 'SELECT ' . $name . '.CURRVAL FROM DUAL';
            // will throw an exception if this sequence does not exist
            $stmt = $this->query($sql);
            $result = $stmt->fetch(\PDO::FETCH_ASSOC);
            if ($result !== false && isset($result['CURRVAL'])) {
                return (int) $result['CURRVAL'];
            }
    }
    // OCI8 driver does not provide support of lastInsertId
    return null;
}