Fix fetch mode usage.

[silvioq]

Use PDO::FETCH_BOTH as default. PDO::ATTR_DEFAULT_FETCH_MODE is an invalid fetch mode.

This commit fixes $stmt->fetch(); without fetch style, that returns false (at least in php 7.1). PDO::ATTR_DEFAULT_FETCH_MODE is invalid for fetch. (see http://php.net/manual/en/pdostatement.fetch.php)

Now, fetch without fetch style uses default fetch for connection or PDO::FETCH_BOTH if it is not defined.

[yajra]

Looks good and doesn't seem to break my app. Thanks!

[silvioq]

Thanks!