Handling of multiple features being passed to cargo-metadata

[JaimeValdemoros]

Describe the bug
Multiple features are passed to cargo-metadata as --features foo bar rather than --features foo,bar

To Reproduce

$ cargo new krates-test && cd krates-test
$ cargo add krates@0.10.0
$ cat <<EOF >src/main.rs
use krates::{Builder, Cmd, Krates};
fn main() {
    let mut cmd = Cmd::new();
    cmd.manifest_path("./Cargo.toml");
    cmd.features(vec!["foo".to_string(), "bar".to_string()]);
    let _: Krates = Builder::new().build(cmd, |_| {}).unwrap();
}
EOF
$ cat <<EOF >>Cargo.toml

[features]
foo = []
bar = []
EOF
$ cargo --quiet run
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Metadata(CargoMetadata { stderr: "error: Found argument 'foo' which wasn't expected, or isn't valid in this context\n\nUSAGE:\n    cargo metadata --features <FEATURES>... --format-version <VERSION> --manifest-path <PATH>\n\nFor more information try --help\n" })', src/main.rs:8:55
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Additional context
Replacing vec!["foo".to_string(), "bar".to_string()] with vec!["foo,bar".to_string()] causes it to run successfully.

I suspect this is due to the following lines - opts.append(&mut cmd.features); should instead be opts.push(cmd.features.join(","));:

krates/src/builder.rs

Lines 158 to 161 in ad78f9e

	if !cmd.features.is_empty() {
	opts.push("--features".to_owned());
	opts.append(&mut cmd.features);
	}

.