update: show process command in debug log

src/Process.php

@@ -15,6 +15,7 @@ class Process {
             $desc[1] = array('pipe', 'w'); // stdout
             $desc[2] = array('pipe', 'w'); // stderr
         }
+        logging::debug('Process command -> `' . implode(' ', $command) . '`');
         $this->process = proc_open($command, $desc, $pipes, null, $env); // start process
         if (is_resource($this->process)) { // process start success
             $this->pid = proc_get_status($this->process)['pid'];