Codeblocks are beeing emojified

[Nicolas Peugnet]

for instance sending this code block:

```
:user-agent:mime-version:date:message-id:dkim-signature
```

results in this message where :date: is converted into 📅 emoji:

09:58:33 <Nicolas P> :user-agent:mime-version📅 message-id:dkim-signature

I can look into fixing it soon.