Fixed: Cleanup Temp files after backup creation

Fixes #925

(cherry picked from commit 7f0b708cb9f16a0116199625a2a5b4e67049be6a)

src/NzbDrone.Core/Backup/BackupService.cs

@@ -90,6 +90,8 @@ namespace NzbDrone.Core.Backup
 
             _archiveService.CreateZip(backupPath, _diskProvider.GetFiles(_backupTempFolder, SearchOption.TopDirectoryOnly));
 
+            Cleanup();
+
             _logger.ProgressDebug("Backup zip created");
         }