Fix compatibility with HasFactory (#25)

Author: stefanzweifel

.gitignore

@@ -2,6 +2,7 @@
 .php_cs
 .php_cs.cache
 .phpunit.result.cache
+.phpunit.cache
 .phpunit.cache/test-results
 build
 composer.lock

src/Models/Send.php

@@ -78,7 +78,7 @@ class Send extends Model
         'rejected_at' => 'immutable_datetime',
     ];
 
-    protected static function newFactory(): SendFactory
+    protected static function newFactory()
     {
         return new SendFactory();
     }