Incorrect php open tag

[MiquelAdell]

On the file:
ds-gallery-categories-navigation-template.php
line 16 there is a <? open tag that (at least in my instalation) does not get correctly rendered.

Changing that to <?php solves the issue.

Thanks!

[MiquelAdell]

I've created a pull request ( #58 ) fixing this. I think.

It's my first pull request so please excuse me (and let me know) if something is not as it should.

Thanks!