Fixes/backup issues (#51)

* Fix: Error related to undefined Backup::size()

* Fix: Disable signals if PCNTL isn't loaded to avoid fatal error (Fixes SIGINT is not defined on environments that are missing the PCNTL library)

app/Http/Controllers/V1/Admin/Backup/BackupsController.php

@@ -36,7 +36,7 @@ class BackupsController extends ApiController
                         return [
                             'path' => $backup->path(),
                             'created_at' => $backup->date()->format('Y-m-d H:i:s'),
-                            'size' => Format::humanReadableSize($backup->size()),
+                            'size' => Format::humanReadableSize($backup->sizeInBytes()),
                         ];
                     })
                     ->toArray();