Bug fix for function updateLob: array to string conversion error.

I was trying to execute the following code:

```php
public function testUpdateBlob($id)
{
        $filename = 'files/file.xlsx';
        $handle = fopen($filename, 'rb');
        
        $id = DB::table($this->_model->getTable())->whereId($id)->updateLob(
                array('name'=>'test'),
                array('blob' => fread($handle, filesize($filename)))
        );    
        fclose($handle);
}
```

and the error was: ErrorException: Array to string conversion.
Changing it to the correct getter instead of using the property directly resolved the problem.