winston module not behaving properly

How can I update log file when using Winston to handle logging for node.js. Below is the code which I tried. Only first time the data is getting saved in log file.

var logger = new (winston.Logger)({
   transports: [
      new (winston.transports.Console)(),
      new (winston.transports.File)({ filename: '2012-07-09.log' })
  ]
});

logger.log('info', 'Test Log Message', { anything: 'This is metadata' });

Im using Node version 0.10.10 and winston 0.7.1

Any help on this will be really helpful. Thanks