Fix compatibility with FreeBSD tar

This change fixes #677 by adding `-f -` to the tar command.


The problem in #677 still exists, so the issue should be reopened. As the thread describes, running tar with `-f -` fixes the issue on FreeBSD, but it was unclear how that would affect Linux / GNU tar.

I've just tested the `-f -` fix with:
- FreeBSD tar (bsdtar)
- OS X tar (which is also bsdtar, but oddly enough does not seem to suffer from the same issue)
- GNU tar

All three could handle the `-f` flag without a problem, so it seems this change does not break compatibility with Linux / GNU tar.