Update Forum.php
Update Forum.php

Requirements::themedCSS needs valid filename of a css file. 
The css filename is not "forum.css", but "Forum.css"
gordonbanderson/silverstripe-forum,mandrew/silverstripe-forum,camfindlay/silverstripe-forum,Olliepop/silverstripe-forum,gordonbanderson/silverstripe-forum,mandrew/silverstripe-forum,Olliepop/silverstripe-forum,camfindlay/silverstripe-forum