Request parameters lost in unittest

Hello,

I am using dingo with lumen 5.2.6.

Request (post/get/http headers) are lost when making request to endpoint from unit test.

```
$request = $this->post('api/user/access_token',[
'client_id' => {ID},
'client_secret' => {SECRET},
'grant_type' => 'client_credentials'
]);
```

in `LumenServiceProvider.php` file when i print $request on line 35, i can see my post data there, but after this it is gone.