Change 'fire' to 'dispatch' when mocking application events

Mock 'dispatch' method instead of 'fire' in EventDispatcher due to Laravel 5.4 change.

src/Illuminate/Foundation/Testing/Concerns/MocksApplicationServices.php

@@ -101,7 +101,7 @@ protected function withoutEvents()
     {
         $mock = Mockery::mock(EventsDispatcherContract::class);
 
-        $mock->shouldReceive('fire')->andReturnUsing(function ($called) {
+        $mock->shouldReceive('dispatch')->andReturnUsing(function ($called) {
             $this->firedEvents[] = $called;
         });