Update our Cargo.lock file to remove the deprecated and removed [root] section

This is causing build errors on Travis, which picked up the newest cargo nightly a week ago. As pointed out by Sebastian, the error appears to be due to cargo issue #4563, which completely removed the [root] section of Cargo.lock files. Often, historically, the [root] section was used with an arbitrary non-existent crate, before cargo workspaces were implemented. However, our Cargo.lock file contains not only a [root], but one which points to a non-arbitrary crate, tor_util. IIUC, we'll just need to remove that section.

(While we're at it, we may want to update to the newest libc dependency.)

I think we'll need to backport this to 0.3.0.x, since no newer cargos will build something with a [root] section.