PHP round() precision errors

In the [pun_attachment/include/attach_func.php](https://github.com/punbb/extensions/blob/master/pun_attachment/include/attach_func.php#L204) extension file in line 204 onwards, reduce the rounding of digits from 2 to 1 to avoid large irrational decimals.
![round_2](https://user-images.githubusercontent.com/2995044/32981707-17edf9d8-cc9f-11e7-9cd0-03927ca818fe.png)
