code: function defaultMockFilename(config, req) {
      var reqData = prismUtils.filterUrl(config, req.url);
      // include request body in hash
      if (config.hashFullRequest(config, req)) {
        reqData = req.body + reqData;
      }
  
      var shasum = crypto.createHash('sha1');
      shasum.update(reqData);
      return shasum.digest('hex') + '.json';
    }
docs: This is the default implementation to generate a filename for the recorded
  responses.  It will create a sha1 hash of the request URL and optionally,
  the body of the request if the `hashFullRequest` config is set to true.
  This function can be overidden in config with the responseFilenameCallback
  setting.