edition: Update io_jail crate to 2018 edition
edition: Update io_jail crate to 2018 edition

Separated out of CL:1513058 to make it possible to land parts
individually while the affected crate has no other significant CLs
pending. This avoids repeatedly introducing non-textual conflicts with
new code that adds `use` statements.

TEST=cargo check
TEST=cargo check --all-features
TEST=cargo check --target aarch64-unknown-linux-gnu

Change-Id: Id5f2c4f9005498e2357bec5878761c33d2bc3d8b
Reviewed-on: https://chromium-review.googlesource.com/1519697
Commit-Ready: David Tolnay <1480464b87745a0822a0e8b7545ca981d8e7352e@chromium.org>
Tested-by: David Tolnay <1480464b87745a0822a0e8b7545ca981d8e7352e@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: David Tolnay <1480464b87745a0822a0e8b7545ca981d8e7352e@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm