homebrew does internal caching in ARGV that prevents us from doing the
`ARGV.clear; ARGV << 'newarg'` trick twice.
rather than try to further reach in to homebrew's innards, i figure it's
better to just pass multiple arguments down to homebrew code at once,
since it already supports that
refs #47
this delegates to homebrew's uninstall to get its work done. vanilla
`brew uninstall` actually works, but this gives us a more consistent
interface.
as discussed in #47
phinze