title: Get old messages after bot reboot (Discord bot, NodeJS)
body: <p>I'm trying to make a Discord Bot and I have some issues. 
  I want a way to get all messages of a channel but, after bot reboot, he doesn't "see" the old messages.
  Here is an example:</p>
  
  <pre><code>const commando = require('discord.js-commando');
  
  module.exports = class nbMess extends commando.Command{
      constructor(client) {
          super(client, {
              name: 'nbmsg',
              group: 'admin',
              memberName: 'nbmsg',
              description: 'Return number of messages in a channel'
          });
      }
      async run(msg, args){
          msg.channel.send(`Number of messages : ${msg.channel.messages.size}`);
      }
  }
  </code></pre>
  
  <p>So, I send 3 random messages, and after this, I boot the bot and launch the command.
  And the result is 1, for the message that call the command.</p>