Is your feature request related to a problem? Please describe.
Without a Cargo.lock, building the hyper crate itself (i.e., as a cdylib for curl) can be difficult to do in a reproducible manner and/or in environments where offline building is required.

Describe the solution you'd like
Cargo.lock being removed from .gitignore and distributed upstream.

Describe alternatives you've considered
Downstream vendors can make their own Cargo.lock files. This is currently being done in NixOS/nixpkgs#357552.

Additional context
Previously, the Cargo team recommended against having Cargo.lock files distributed by libraries. As of last year, they have changed this advice to "recommend people do what is best for their project".