title: Change prefix for discord bot in javascript
body: <p>I'm making a bot and want to have a prefix to call the bot. It works to change when you don't have groups. But how do I change the prefix "!" when I use groups?</p>
  
  <p>My main code    </p>
  
  <pre><code>const commando = require('discord.js-commando');
  const bot = new commando.Client();
  const prefix = ":D";
  
  bot.registry.registerGroup('random', 'Random');
  bot.registry.registerCommandsIn(__dirname + "/commands");
  
  bot.login('Botcode'
  );
  </code></pre>
  
  <p>My group</p>
  
  <pre><code>const commando = require('discord.js-commando');
  
  class DiceRollCommand extends commando.Command {
    constructor(client) {
      super(client, {
        name: 'roll', 
        group: 'random',
        memberName: 'roll',
        description: 'Roll a die'
      });
    }
  
    async run(message, args){
      var roll = Math.floor(Math.random() * 6) + 1;
      message.reply("You rolled a " + roll);
    }
  }
  
  module.exports = DiceRollCommand;
  </code></pre>