Update Rust crate assert_cmd to v2.0.16 #259

Job	Run time
cargo check (ubuntu-latest)	14s
cargo clippy -- -D warnings (ubuntu-latest)	17s
cargo check (macOS-latest)	18s
cargo clippy -- -D warnings (macOS-latest)	17s
Code Coverage (ubuntu-latest, unix)	2m 4s
cargo check (windows-latest)	53s
Code Coverage (macos-latest, macos)	2m 10s
cargo clippy -- -D warnings (windows-latest)	53s
Code Coverage (windows-latest, windows)	6m 7s
cargo fmt --all -- --check	12s
GNU test suite	1m 43s
cargo test (ubuntu-latest)	48s
cargo test (macOS-latest)	3m 5s
cargo test (windows-latest)	3m 17s
	22m 18s

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