Update Pulse.php (#76)

Fix problem doing "composer require laravel/pulse"

 Uncaught TypeError: Laravel\Pulse\Pulse::Laravel\Pulse\{closure}(): Argument #1 ($event) must be of type Illumi
nate\Events\Dispatcher, Illuminate\Events\NullDispatcher given, called in /var/www/sapere/sapere/vendor/laravel/framework/src/Illuminate/Container/Container.php on line 1302 and defined in /var/www/sapere/sapere/vendor/laravel/pulse/src/Pulse.php:119        
Stack trace:

src/Pulse.php

@@ -6,7 +6,7 @@
 use DateTimeInterface;
 use Illuminate\Contracts\Auth\Authenticatable;
 use Illuminate\Contracts\Foundation\Application;
-use Illuminate\Events\Dispatcher;
+use Illuminate\Contracts\Events\Dispatcher;
 use Illuminate\Support\Collection;
 use Illuminate\Support\Lottery;
 use Illuminate\Support\Traits\ForwardsCalls;