message: set useQuerystring to true
  PHP-style array argument is never valid in Slack API
diff: @@ -251,6 +251,7 @@ module.exports = function(bot, config) {
  bot.debug('** API CALL: ' + url);
  var params = {
  url: url,
  + useQuerystring: true,
  headers: {
  'User-Agent': bot.userAgent(),
  }
  