Fixed test for unix platform

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Related tickets | 
| License       | MIT

The last slash need also to be replace by `DIRECTORY_SEPARATOR`.

```php
dirname(dirname(__DIR__)) . DIRECTORY_SEPARATOR . 'src' . DIRECTORY_SEPARATOR . 'config' . DIRECTORY_SEPARATOR,
```