message: update example of postgresql
diff: @@ -6,25 +6,13 @@ go(function () {
  $pg = new Swoole\Coroutine\PostgreSql();
  $conn = $pg -> connect ("host=127.0.0.1 port=5432 dbname=test user=wuzhenyu password=");
  $result = $pg->query($conn, 'SELECT * FROM test;');
  - $arr = $pg->fetchAll($result);
  + $arr = $pg->fetchAll($result);// the same with affectedRows(),fetchObject(),fetchAssoc(),fetchArray(),fetchRow()
  var_dump($arr);
  //$numRows = $pg->numRows($result);
  //var_dump($numRows);
  });
  -
  -go(function () {
  -
  - $pg = new Swoole\Coroutine\PostgreSql();
  - $conn = $pg -> connect ("host=127.0.0.1 port=5432 dbname=test user=wuzhenyu password=");
  - $result = $pg->query($conn, 'SELECT * FROM test;');
  - $arr = $pg->fetchObject($result);
  - var_dump($arr);
  -
  -});
  -
  -
  go(function () {
  $pg = new Swoole\Coroutine\PostgreSql();
  