Fix running scheduled search index job. (#104)

Arguments need to be passed as an array since passing shell commands as a string to the Process component is deprecated since Symfony 4.2. Related Grav fix which is also needed for this patch to work properly: getgrav/grav@1661dc9

This also finally fixes issue #81.

tntsearch.php

@@ -110,7 +110,7 @@ public function onSchedulerInitialized(Event $e): void
             $scheduler = $e['scheduler'];
             $at = $this->config->get('plugins.tntsearch.scheduled_index.at');
             $logs = $this->config->get('plugins.tntsearch.scheduled_index.logs');
-            $job = $scheduler->addCommand('bin/plugin tntsearch index', [], 'tntsearch-index');
+            $job = $scheduler->addCommand('bin/plugin', ['tntsearch', 'index'], 'tntsearch-index');
             $job->at($at);
             $job->output($logs);
             $job->backlink('/plugins/tntsearch');