Support Cargo.toml with profile overrides (by using newer version of cargo)

[evan-dickinson]

Cargo version 1.41 stabilized profile overrides. But cargo-geiger still considered the feature unstable. Running geiger on a crate that uses profile overrides was failing with this error:

error: failed to parse manifest at `Cargo.toml`

Caused by:
  feature `profile-overrides` is required

this Cargo does not support nightly features, but if you
switch to nightly channel you can add
`cargo-features = ["profile-overrides"]` to enable this feature

To fix the problem, I incremented the version of cargo to 0.42.0. And I also ran cargo update to update other dependencies, too.

[evan-dickinson]

I'm not sure why the CI tests failed. I did cargo test --all and it succeeded on my computer (macOS 10.14).

[anderejd]

Thanks for the PR.

It seems like the master branch is failing the tests as well on Azure now. Will look into it later this week.

[anderejd]

The new test snapshot files seems to have a different naming than the existing ones...

[anderejd]

Let's roll with the new naming of the test snapshots. Feel free to delete the old snapshots and commit new ones if they look correct.

[anderejd]

Superseded by #98.