Apply Laravel code style

Author: jeromegamez

src/FirebaseProjectManager.php

@@ -25,7 +25,7 @@ public function __construct(Container $app)
         $this->app = $app;
     }
 
-    public function project(string $name = null): FirebaseProject
+    public function project(?string $name = null): FirebaseProject
     {
         $name = $name ?? $this->getDefaultProject();
 

tests/FirebaseProjectManagerTest.php

@@ -289,7 +289,7 @@ public function it_uses_the_laravel_cache_as_auth_token_cache(): void
         $this->assertInstanceOf(CacheItemPoolInterface::class, $property->getValue($factory));
     }
 
-    private function factoryForProject(string $project = null): Factory
+    private function factoryForProject(?string $project = null): Factory
     {
         $project = $this->app->make(FirebaseProjectManager::class)->project($project);