As you likely know, it is always a good practice to use the latest version of software.
Especially if security flaws are fixed in the latest version.

So if anything is “the culprit”, I would say it is GoDaddy and not avast.

cPanel 11.40.1.11 (as GoDaddy is using) was released on 04-02-2014
Several other version have been released since then.
The latest on is 11.44.1.7 released… Yesterday!

https://documentation.cpanel.net/display/ALD/Change+Logs
As you can see there, several security flaws have been fixed.

Ofcourse there will be people going into discussion if a av should block websites that use outdated software.
In my opinion, I say yes. It is helping to protect users/visitors and the website owners.

You can always request avast to allow your domain through the contact form:
www.avast.com/contact-form.php

I am asking you to change the text on your website about this, because now you know what is going on.
Perhaps even put a link to this thread there.

Just to avoid misunderstandings, I am not working for avast.
Just like Pondus, you and most people here on this webboard, I am just a user with some (since 1983) experience with computers.