docs: function(bucket, key, version, localPath) {
          return S3.getObject({
              Bucket: bucket,
              Key: key,
              VersionId: version
          }).promise().then(function(data) {
              return new Promise(function(resolve, reject) {
                  fs.writeFile(localPath, data.Body, function(err) {
                      if (err) return reject(err);
                      resolve(localPath);
                  });
              });
          });
      }