Fix for String not found error in Unix/Linux

[kavanpancholi]

Fix for below error

PHP Fatal error:  Uncaught Error: Class 'String' not found in /home/vagrant/Code/php-boilerplate/ProcessList.phpclass:220
Stack trace:
#0 /home/vagrant/Code/process/ProcessList.phpclass(128): ProcessList->UnixPs()
#1 /home/vagrant/Code/process/ProcessList.phpclass(50): ProcessList->Refresh()
#2 /home/vagrant/Code/process/process.php(20): ProcessList->__construct()
#3 {main}
  thrown in /home/vagrant/Code/process/ProcessList.phpclass on line 220