Kill the running process and remove the PID/lock file.

def kill(self):
        """
        Kill the running process and remove the PID/lock file.
        """
        try:
            kill(int(self.get()), 9)
            
        # Failed to kill the process
        except Exception as e:
            self.die('Failed to kill process: {}'.format(str(e)))
            
        # Remove the stale PID file
        self.remove()