array_get is incompatible with laravel 6.0+

[AbyssWaIker]

At lines 33, 34, 42 of src/ApiTesterCotroller.php and 268 of src/ApiTester.php function array_get is used. It breaks in any versions of Laravel newer than 6.0. It's fixed by replacing it with function Arr:get (and adding "use Illuminate\Support\Arr;"). I would make a new branch for newer versions of Laravel, but I'm too shit with git to make a proper pull request