napi: fix build error in cargo-auditable

[JohnRTitor]

As reported #702
when trying to build via cargo auditable build --release --lib --bin=lightningcss --features="cli" build fails with the following error.

   Compiling lightningcss v1.0.0-alpha.55 (/home/masum/Dev-Environment/lightningcss)
    Building [=======================> ] 169/171: lightningcss                            thread 'main' panicked at cargo-auditable/src/collect_audit_data.rs:77:9:
cargo metadata failure: error: Package `lightningcss-napi v0.1.0 (/home/masum/Dev-Environment/lightningcss/napi)` does not have feature `rayon`. It has an optional dependency with that name, but that dependency uses the "dep:" syntax in the features table, so it does not have an implicit feature with that name.

This patch fixes the bug and the build succeeds on cargo auditable.

[JohnRTitor]

Should close #702