Fix DummyFilter for "Apex" Theme

[Andrew Jenkins]

Error when clicking on either of the first two posts - any post with tags.

File "themes/postachio/theme-apex/theme.html", line 195, in top-level template code <li><a href="/tag/{{ tag }}">{{ tag|format_tag(link=False, humanize=True) }}</a></li> TypeError: DummyFilter() got an unexpected keyword argument 'link'