Add support for the new cargo lockfile format

[jonasbb]

Recently cargo nightly started produces lockfiles with the new format (rust-lang/cargo#7579).

Tarpaulin fails to compile tests, if it encounters such a log file. One instance can be found here. Tarpaulin fails with this message:

Error: "Failed to compile tests! Error: failed to parse lock file at: /home/travis/build/jonasbb/serde_with/Cargo.lock"

In my case I run Tarpaulin on a library and therefore do not commit the lockfile, which is why nightly now uses the new lockfile format.

[xd009642]

There's now a new cargo_update branch this updates the tarpaulin cargo dependency to 0.40.0 and may solve the issue. I'll try it myself when I've got time to but in the meantime if you test it and report back I can fast track the merge/release 👍

[HaoXuan40404]

Same problem too

[jonasbb]

@xd009642 I started a try build with tarpaulin from the new branch. It passed on all Rust versions.
https://travis-ci.org/jonasbb/serde_with/builds/621365163
So this would fix the issue for me.

[xd009642]

Awesome, well since it doesn't affect anything in terms of existing build functionality I've just pushed out another release. If you could try it out and confirm it now works this issue can be closed 😄

[xd009642]

It's now released in 0.10.0 so closing this