code: function getFileHash(filePath, callback) {
    var stream = fs.ReadStream(filePath);
    var md5sum = crypto.createHash('md5');
  
    stream.on('data', function(data) {
      md5sum.update(data);
    });
  
    stream.on('end', function() {
      callback(md5sum.digest('hex'));
    });
  }
docs: given the path to a local file being streamed, returns back the MD5 hash to quickly check if a file's contents have changed.