Auto merge of #2680 - alexcrichton:update-toml, r=brson

Update TOML parser to pick up a bugfix

Cargo has previously accepted invalid TOML as valid, but this bugfix should fix
the problem. In order to prevent breaking all crates immediately toml-rs has a
compatibility mode which emulates the bug that was fixed. Cargo will issue a
warning if this compatibility is required to parse a crate.

diff --cc Cargo.lock
Simple merge

diff --cc Cargo.toml
Simple merge

diff --cc src/cargo/util/toml.rs
Simple merge