Reuse $this->app in service provider (#22)

Author: spawnia

src/LaravelMsGraphMailServiceProvider.php

@@ -41,7 +41,7 @@ public function boot(): void
             throw_unless(filled($config['from']['address'] ?? []), ConfigurationMissing::fromAddress());
 
             return new MicrosoftGraphTransport(
-                app()->make(MicrosoftGraphApiService::class)
+                $this->app->make(MicrosoftGraphApiService::class)
             );
         });
     }