Fix: NullOutput clear #72 (#89)

Fix:  #72
When starting the command schedule:start without -v the output will be NullOutput which doesn't contain the clear function

Command/ExecuteCommand.php

@@ -191,8 +191,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
 
             $progress->finish();
 
-
-            if(!is_a($this->output, StreamOutput::class))
+            if(method_exists($sectionProgressbar, 'clear'))
             {$sectionProgressbar->clear();}
 
             $io->section('Finished Executions');