Keep curly braces around for string substitution

Author: schlessera

src/Core_Command.php

@@ -694,7 +694,7 @@ private function multisite_convert_( $assoc_args ) {
 \$base = '{$assoc_args['base']}';
 define( 'DOMAIN_CURRENT_SITE', '{$domain}' );
 define( 'PATH_CURRENT_SITE', '{$assoc_args['base']}' );
-define( 'SITE_ID_CURRENT_SITE', $site_id );
+define( 'SITE_ID_CURRENT_SITE', {$site_id} );
 define( 'BLOG_ID_CURRENT_SITE', 1 );
 EOT;