Update comments.php

WordPress debugger sees an undefined constant is the callback function name isn't wrapped in single quotes. Doesn't affect operation of theme as far as I can tell, but WP unit testing suggests addressing these kinds of things.

comments.php

@@ -22,7 +22,7 @@ if ( post_password_required() ) {
           'style'             => 'div',
           'short_ping'        => true,
           'avatar_size'       => 40,
-          'callback'          => bones_comments,
+          'callback'          => 'bones_comments',
           'type'              => 'all',
           'reply_text'        => 'Reply',
           'page'              => '',