Switch numeric capability 8 to 'manage_options' to fix deprecation notice

Fixes this PHP Notice: has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0! Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /wp-includes/functions.php on line 3006

http://codex.wordpress.org/Roles_and_Capabilities#User_Levels