Update codebase to L5.4 (#367)

config/services.php

@@ -29,10 +29,8 @@ return [
         'region' => 'us-east-1',
     ],
 
-    'stripe' => [
-        'model'  => Pterodactyl\Models\User::class,
-        'key'    => env('STRIPE_KEY'),
-        'secret' => env('STRIPE_SECRET'),
+    'sparkpost' => [
+        'secret' => env('SPARKPOST_SECRET'),
     ],
 
 ];