anchor.diff:        url += HttpHelper.buildQueryString(query);
       }
       
  -    return bot.plugin.httpClient.get(url).then((response) {
  +    return bot.plugin.httpClient.get(url, headers: headers).then((response) {
         if (response.statusCode != 200) {
           throw new HttpError("failed to fetch JSON", response.statusCode, response.body);
         }
  
positive.code:       url += HttpHelper.buildQueryString(query);
      }
      
      return bot.plugin.httpClient.get(url).then((response) {
        if (response.statusCode != 200) {
          throw new HttpError("failed to fetch HTML", response.statusCode, response.body);
        }
  
negative.code:       url += HttpHelper.buildQueryString(query);
      }
  
      return bot.plugin.httpClient.get(url, headers: headers).then((response) {
        if (response.statusCode != 200) {
          throw new HttpError("failed to fetch data", response.statusCode, response.body);
        }
  