Fix signature of HandleErrors middleware

In Laravel 5.8, the `Container::tagged()` method was changed to return
an iterator [1].

We only use the result for iteration, or, in this case, to pass a bunch
of "reporters" to the error handler middleware, therefore we need to
accept an iterable here.

[1]: https://laravel.com/docs/5.8/upgrade#container-generators

src/Http/Middleware/HandleErrors.php

@@ -41,7 +41,7 @@ class HandleErrors implements Middleware
      */
     protected $reporters;
 
-    public function __construct(Registry $registry, HttpFormatter $formatter, array $reporters)
+    public function __construct(Registry $registry, HttpFormatter $formatter, iterable $reporters)
     {
         $this->registry = $registry;
         $this->formatter = $formatter;