Actually get the correct full version for DMG

This is what I get for trying to be smart and pushing a change from the Linux
box because the fix was 'obvious'. Duh. It was not. In order to get the real
full version including the git hash we always have to pass 'linux' to the
gen-version script, even on a Mac.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>