Update dependenies

Between toml:0.5.6 and toml:0.5.7 a parse error message changed from

    config parsing failed: invalid number at line 2 column 15

to

    config parsing failed: invalid TOML value, did you mean to use a quoted string? at line 2 column 15

causing test_invalid_toml_from_string to fail on fresh builds. Update
all dependencies and adjust this test accordingly.

But because of a new lock file format in Rust 1.38 [1], "Cargo update"
now produces a lock file that Cargo from Rust 1.36 can't read, causing
build pinned-linux with MSRV 1.36 to fail. Fortunately cargo-lock [2]
can forge a "v1" format from the new file.

[1] rust-lang/cargo#7579
[2] https://github.com/rustsec/cargo-lock