wreq and wreq-util are pre-release crates whose public API shifts
between rc releases. The caret version requirements let a fresh resolve
pull a newer rc where CertStore moved out of tls, cert_store was renamed
to tls_cert_store, and the Emulation builder changed. That broke
cargo build --features stealth (issue #234).
Pin to =6.0.0-rc.28 and =3.0.0-rc.10, the versions wreq_client.rs is
written against, so the build always resolves to a compatible API.