Changed capability requirement to a more suitable capability

This allows themes or users that have disabled the plugin and theme editor to use the plugin. Even while logged in as admin, if this plugin is enabled while the editor is disabled you get the following error.

`You do not have sufficient permissions to access this page.`

Please see the codex for more information -

http://codex.wordpress.org/Editing_wp-config.php#Disable_the_Plugin_and_Theme_Editor