Use contract to resolve dependency conflict in pulse:check

[joeyrush]

This resolves the following error message when running php artisan pulse:check in an application that has a custom event dispatcher:

Laravel\Pulse\Commands\CheckCommand::handle(): Argument #3 ($event) must be of type Illuminate\Events\Dispatcher, Lorisleiva\Actions\EventDispatcherDecorator given, called in /Users/joerushton/projects/newtickets/vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php on line 36

[driesvints]

This seems to break the test suite

[timacdonald]

Gonna see if we can get this going again over in #376