Update finediff.php

Fixed bug where "abc def" and "abc def ghi" when using the wordDelimiters would result in "c4d3i7:def ghi" rather than "c7i4: ghi". The issue was that whitespace was being treated as being part of a word, so the lack of trailing whitespace after "def" meant that it didn't match "def " and therefore wasn't recognised as being a valid match. The solution is to create separate word fragments and whitespace fragments.