[Plugin: Contact Form 7] Having only Admin editing rights

I want to ensure that only Administrators can can access the plugin and edit the Contact Forms.

I have placed the lines as instructed in Contact Form 7 tips within the wp_config.php file. This has not taken effect. Not sure, if they need to be anywhere special, so I have just added them to the end:

Here is the extract of the bottom half of the file.

/** Sets up WordPress vars and included files. */
require_once(ABSPATH . ‘wp-settings.php’);

/** Wellsites: restricting access to Contact Form 7 **/
define( ‘WPCF7_ADMIN_READ_CAPABILITY’, ‘manage_options’ );
define( ‘WPCF7_ADMIN_READ_WRITE_CAPABILITY’, ‘manage_options’ );
?>

Have I included them correctly? Is there a step I’m missing to make these changes take effect?

Thank you in advance for your help.

PS. Are there any plans to add role capability as an option within wordpress? Just like NextGen Gallery?