Added fix for the Laravel 5.4

[Wolg]

No description provided.

[barryvdh]

Can you explain what this does? And don't this works on pre-5.4

[Wolg]

@barryvdh I had troubles migrating an app using cors to Laravel 5.4 this morning.
The code below doesn't do anything:
$this->app['router']->middleware('cors', HandleCors::class);
If we print results of $this->app['router']->getMiddleware() we can see that "cors" was not registered. And we have to add 'cors' => \Barryvdh\Cors\HandleCors::class into app Kerner's $routeMiddleware.
Solution here would be to use aliasMiddleware method which does the thing.
https://github.com/laravel/framework/blob/5.4/src/Illuminate/Routing/Router.php#L677

[barryvdh]

Added check here to see if method exists, for <L5.4: e05c3ba