change command for Rust to `cargo run`

[danielrab]

Cargo is part of the default toolchain. Using rustc directly will fail if there's any external packages used. Files other than main in a Rust project are usually not meant to be executed directly. Because of all of the above, running cargo run has a much higher chance to produce the desired result.

[danielrab]

forgot to check when making the PR and made a duplicate of https://github.com/formulahendry/vscode-code-runner/pull/354