Fix container setting closure

Hi again! 
I think that a feature documented on [README](https://github.com/cloudson/Config/blob/develop/README.md) is not working. 
I wrote the same example found in the doc:

conf.ini: 

```ini
db_driver = "mysql"
db_host   = "localhost"
db_name   = "my_database"
db_user   = "my_user"
db_pass   = "my_pass"
db_dsn    = "[db_driver]:host=[db_host];dbname=[db_name]"

```
index.php: 

```php
<?php

require __DIR__.'/vendor/autoload.php';

$c = new Respect\Config\Container(__DIR__.'/conf.ini');
$c->connection = function() use($c) {
    return new PDO($c->db_dsn, $c->db_user, $c->db_pass);
};
echo get_class($c->connection); //PDO

```

And I had...
```bash
PHP Warning:  trim() expects parameter 1 to be string, object given in library/Respect/Config/Container.php on line 272

... 
PHP Fatal error:  Uncaught exception 'InvalidArgumentException' with message 'Item connection not found' in library/Respect/Config/Container.php:103
```
If you create a container object without pass a file/string on constructor, it works.

well, I created a test case (use it to break tests of version 1.0.1) and a possible fix.

:cloud: