Add 'index' => 'viewIndex' to resourceAbilityMap()

Re-submitting laravel#28881 because its merge into master resulted in no files changed

src/Illuminate/Foundation/Auth/Access/AuthorizesRequests.php

@@ -105,6 +105,7 @@ public function authorizeResource($model, $parameter = null, array $options = []
     protected function resourceAbilityMap()
     {
         return [
+            'index' => 'viewAny',
             'show' => 'view',
             'create' => 'create',
             'store' => 'create',