Can't install last version of Wagon. Only v.1.5.8 seems installable

Hi,

I'm struggling at the very beggining of the "Quick Start" Guide, as I simply cannot install the latest version of wagon (3.0.5 at the time i'm writing this).
I'm using Ubuntu 20.04 and I installed ruby following this guide : https://gorails.com/setup/ubuntu/20.04

Then I try to install wagon using gem install locomotivecms_wagon
but it installs the version 1.5.8.

So I try forcing the latest version using gem install locomotivecms_wagon -v 3.0.5 but i got the following error :

ERROR: While executing gem ... (NoMethodError)
undefined method `request' for nil:NilClass

Can somebody help me here ? I really don't understand what's going on. I never experienced such issues with other standalone gem installations.

Thanks a lot,

Grégoire