Remove 'n prev' on cleanup

It was removed from 'n'

Author: Ilya Radchenko

worker.js

@@ -90,11 +90,10 @@ module.exports = {
         path.join(__dirname, 'node_modules/n/bin'),
         ret.env.N_PREFIX + '/bin'
       ]);
-      
+
       var version = config.runtime === 'custom' ? config.customVersion : config.runtime;
 
       ret.environment = 'n ' + (config.fork === 'io.js' ? 'io ' : '') + version;
-      ret.cleanup = 'n prev';
     }
 
     cb(null, ret);