Fixes #1063. Allows arguments to taps in a Brewfile with:

tap "foo/bar", "https://host/path/to/tap", args: ["force-auto-update"]

Mostly useful for adding --force-auto-update for non-Github taps.

Syntax is an array of arguments, like with brew, rather than a
dictionary like cask - this is because none of the optional arguments
of brew tap take a value right now. In the future, we should be able
to add support for dictionaries as well without needing to change the
format, if that becomes necessary.