message: update mysql example.
diff: @@ -6,6 +6,12 @@ $server = array(
  'password' => 'root',
  'database' => 'test',
  );
  +
  +$db->on('close', function() use($db) {
  + echo "mysql is closed.\n";
  + var_dump($db->close());
  +});
  +
  $r = $db->connect($server, function ($db, $result)
  {
  if ($result === false)
  