Error connecting oracle

I'm trying to perform insert operation on oracle by Laravel (5.6), but it's giving error:

The method I make the insert is this:

public function salvar( Request $request ){
        $agenda = new Agenda();
        $agenda->dt_agenda = $request->input('data');
        $agenda->hr_agenda = $request->input('hora');
        $agenda->nm_pessoa = $request->input('nome');
        $agenda->save();
        $data = date('d/m/Y');
        return view('escala')->with( 'data', $data );
    }

In the config / database.php file it looks like this:

 'default' => env('DB_CONNECTION', 'oracle'),
    ...
    'oracle' => [
                'driver'         => 'oracle',
                'host'           => env('DB_HOST', ''),
                'port'           => env('DB_PORT', '1521'),
                'database'       => env('DB_DATABASE', ''),
                'username'       => env('DB_USERNAME', ''),
                'password'       => env('DB_PASSWORD', ''),
                'charset'        => env('DB_CHARSET', 'AL32UTF8'),
                'prefix'         => ''
            ],

The .env file is properly configured

DB_CONNECTION=oracle
DB_HOST=ipdoservidor
DB_PORT=1521
DB_DATABASE=banco
DB_USERNAME=login
DB_PASSWORD=senha

The error you are giving is:

  

ErrorException (E_WARNING) Declaration of   Yajra \ Oci8 \ Oci8Connection :: causedByLostConnection (Exception $ e) should   be compatible with   Illuminate \ Database \ Connection :: causedByLostConnection (Throwable $ e)

My composer.json looks like this:

"require": {
        "php": ">=7.1.3",
        "barryvdh/laravel-ide-helper": "^2.4",
        "fideloper/proxy": "~4.0",
        "laravel/framework": "5.6.*",
        "laravel/tinker": "~1.0",
        "yajra/laravel-oci8": "5.6.*"
    },