It's easy to get confused by the package cabal-install installing a
tool called `cabal`, while the underlying library is called Cabal.
So, when you run `cabal --version` you are checking which version of
cabal-install you have, and which version of Cabal *it* is using.
However, when you build aura cabal-install isn't used (based on my
reading of it's PKGBUILD), it uses a method that goes straight to
Cabal and it then uses the latest version installed.