chore: attempt to re-use $TMPDIR in `installer-appimage.sh` (#917)
chore: attempt to re-use $TMPDIR in `installer-appimage.sh` (#917)

We currently hardcode the temporary directory location to `/tmp`. Some
Linux systems define `$TMPDIR`, so we should attempt to re-use that
first.

Signed-off-by: Juan Cruz Viotti <4148f5869aa1bcd7efd85b513a5874967e585032@openmailbox.org>
resin-io/etcher,resin-io/etcher,resin-io/herostratus,resin-io/etcher,resin-io/etcher,resin-io/herostratus,resin-io/resin-etcher,resin-io/resin-etcher,resin-io/etcher