def join(channel)
      self.class.post('/channels.join', body: {name: channel, token: @token}).tap do |response|
        raise "error posting message: #{response.fetch('error', 'unknown error')}" unless response['ok']
      end
    end
def join(channel)
      self.class.post('/channels.join', body: {name: channel, token: @token}).tap do |response|
        raise "error posting message: #{response.fetch('error', 'unknown error')}" unless response['ok']
      end
    end
join a channel, needed to post to channel