Makes more sense this way around now Homebrew has migrated across
to 2.1.x & the latest version of that doesn't install as `gpg2`
any more.
Doesn't need to be merged before this PR but for the sake of referencing
the PR introducing the upstream death of the `gpg2` symlink is:
https://github.com/Homebrew/homebrew-core/pull/16580
which_all already runs some checks to see if the file is a file & is executable.
Our usage here inside `self.available?` is mostly a smoke test.
Closes#676.
Signed-off-by: Dominyk Tiller <dominyktiller@gmail.com>
