* gnu/packages/crates-io.scm (rust-rustc-rayon-0.5): New variable. (rust-rustc-rayon-0.4): Inherit from rust-rustc-rayon-0.5.
* gnu/packages/crates-io.scm (rust-rustc-rayon-0.5): New variable. (rust-rustc-rayon-0.4): Inherit from rust-rustc-rayon-0.5.