title: Discord.py - message.content is empty for every message
body: <p>I'm trying to make a discord bot and when I run it locally, it works fine; However when I push it to heroku, it doesn't work because message.content is empty for some reason for every message. It was working fine just a few days ago, but it broke now.</p>
  <p>main.py code:</p>
  <pre><code>@client.event
  async def on_message(message):
      msg = message.content
      print(f'msg1: {msg}')
      print(f'msg: {message}')
  
      if message.author == client.user:
          return
      if message.content == '':
          await message.channel.send('test')
  </code></pre>
  <p>requirements.txt:</p>
  <pre><code>git+https://github.com/Rapptz/discord.py
  dnspython==2.2.1
  async-timeout==4.0.2
  gspread==5.3.0
  oauth2client==4.1.3
  openpyxl==3.0.9
  discord==1.7.3
  </code></pre>