added a wp_head call before the closing head tag

Similar to `wp_footer`, you need this tag for plugins
that add scripts or stylesheets to the `<head>` of the
page. Check out the docs [here](http://codex.wordpress.org/Function_Reference/wp_head).
Merge pull request #3 from ianstormtaylor/patch-2

added a wp_head call before the closing head tag